Kryptonite Messenger Mini With U-Lock Extender review

A lightweight and portable mid-security lock with a much greater lockable area than you might expect

Cycling Weekly Verdict

The Kryptonite Messenger Mini With U-Lock Extender manages to be lightweight and portable while still providing a decent level of security (Sold Secure Silver) and respectable lockable area. There’s a range of thoughtful design elements which include a shackle with a bent foot, the rubberised coating, a dustcover for the lock barrel and the U-lock extender – which increases the lockable area significantly without adding much to the size of the lock. However, the lack of a bike mount and the fact it comes with only two keys does count against it.

Reasons to buy
  • +


  • +

    Extra shackle is genuinely useful

  • +

    Relatively secure

  • +

    Sliding dustcover

Reasons to avoid
  • -

    Doesn’t come with a bike mount

  • -

    Only comes with two keys

You can trust Cycling Weekly. Our team of experts put in hard miles testing cycling tech and will always share honest, unbiased advice to help you choose. Find out more about how we test.

The Kryptonite Messenger Mini With U-Lock Extender is intended as something of a goldilocks lock from the American security brand.

>>>Read more: Best bike locks

It’s designed to be lightweight, while still offering a useful degree of security – as well as being portable, but not to the extent of being so small that it becomes impractical.


It’s worth bearing in mind that no lock is perfectly secure, a determined thief will always be able to get through a lock with the right tools, knowhow, and inclination. A lock has two main purposes, to convince any thieves that there are easier targets to go for and to comply with the wording of your insurance policy so that if your bike is stolen, you will at least be covered.

Sold Secure is an independent lock testing company which vets the security levels of locks on the UK market. They award three levels of ranking: Bronze (generally only good for preventing opportunistic theft), Silver (generally good for moderate crime areas and bikes valued up to £1,000) and Gold (generally good for high crime areas and bikes valued over £1,000). It should be specified in the wording of your insurance policy what level of lock you need to use to be covered.

>>>Read more: How to keep your bike safe

The construction

In all, the build of the lock is really rather good with a range of well thought out design features. Principal among these has got to be the “Bent Foot” shackle. Getting the prongs of the shackle to line up with the holes of the crossbar doesn’t sound like it should be a particularly onerous task, but on competitors, without this "Bent Foot" it somehow always caused me an annoying extra faff.

With the Kryptonite Messenger Mini, one prong is bent to enable the crossbar to slot onto that one first, before swinging over and onto the second prong. A simple design, but it does make the lock significantly quicker and easier to use over the competition with straight shackles.

The crossbar features a sliding dustcover which can cover the barrel of the lock and helps keep out the elements. I haven’t tested the lock for the months and years I would need to in order to meaningfully comment on the long-term durability of this lock, but the sliding dustcover is likely to mitigate any issues with the mechanism seizing.

Kryptonite Messenger Mini With U-Lock Extender

Both the shackle and crossbar feature a smooth, rubberised coating which prevents the lock from chipping the paintwork of your frame. It also felt like it provided a modest amount of insulation when holding the lock with ungloved hands in the cold.

The dimensions of the main lock are 9.5cm x 16.5cm and the extra shackle comes in at 8.3cm x 9.5cm. This means that the lock folds up significantly smaller than an average sized U-lock, such as the Kryptonite Evolution Standard which is 10.2cm x 22.9cm. Despite this, the Kryptonite Messenger Mini With U-Lock Extender actually has a slightly greater lockable area at 236cm2 compared to the Evolution Standard’s 234cm2.

In terms of weight, the Messenger Mini With U-Lock Extender stacks up pretty well too. On its own, the Messenger Mini weighs in at a very impressive 788g, which is bumped up to 1,109g with the addition of the U-Lock Extender. Still a very impressive weight, especially considering the lockable area and security rating.

In use

The extra shackle provided a significant advantage over other portability focused U-locks. It was very easy to secure both the frame and one of the wheels, whereas with other lightweight locks I’ve only tended to be able to secure the frame.

It also helped in providing a bit of extra reach when pushed for space, opening up the possibilities of where I could lock my bike. The shackles are narrower than a standard U-lock though, so I did have to recalibrate my gauge of what is a good object to lock-up to. The bent foot design of the shackle was a real plus, and the sliding dustcover added to my peace of mind when leaving it out in foul conditions.

On the negative side, I was surprised to find that the lock doesn’t come with a bike mount, which is quite a significant omission for a lock with a raison d'être of portability. I would have much appreciated not having to bring a rucksack each time I headed out with the lock – even if it wasn’t taking up much space or adding much weight.

The normal mount that most Kryptonite locks use (the Transit Flexframe-U Bracket) is only compatible with shackles that are 13mm or 16mm in diameter. The Messenger Mini’s shackle is 11mm and so won’t fit this style.

Kryptonite does sell a Transit H-Bar Handlebar Carrier for around £12, and this is compatible with shackles down to 10mm. It mounts the lock onto your handlebar, which could present some compatibility issues depending on your setup, but we haven’t yet had a sample in to properly assess its user friendliness.

Also, only two keys are provided with the lock, although it is possible to order more. Personally, I would be very nervous if I were to misplace a key and only be left with one. Three is the number provided with most locks and is a much better number. That way, if a key is misplaced, you still have some time to wait and see if it will crop up (which it usually does) before having to go to the trouble and expense of ordering a new one.


The Kryptonite Messenger Mini With U-Lock Extender is significantly heavier than the TiGr BLUE Mini+, which weighs in at 470g and has a lockable area of 207cm2, compared to the 1,109g and 236cm2 of the Kryptonite. However, the BLUE Mini+ retails for around £100, which is £25 more than the Messenger Mini With U-Lock Extender. The BLUE Mini+ also has a Sold Secure rating of Bronze compared to the Kryptonite’s Silver.

The Litelok Silver Flexi-U has a claimed weight of 750g, and a lockable area of 311cm2, as well as coming with two straps for mounting it to your bike. As the name suggests, it is flexible so wide lampposts won’t trouble it and its security rating is also Silver. However, the Litelok Silver Flexi-U does retail for £79.99, so it is more expensive than the Kryptonite Messenger Mini With U-Lock Extender and it also takes up a lot more space to provide that lockable area.

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