The first is the '2C' by Busch + Muller. This is a USB charged light that has LEDs around the edges that are bright and do a great job at being seen from quite some distance away. Visibility is good and the light can be seen from quite a few angles.
The Z reflector does exactly what it should when the light is off and means you are compliant with the Highway Code.
The bracket that the light comes with is the permanent bit and fitting is easy. The light then snaps in and out and securely to allow you to charge the light via a USB cable that is included. This looks to be quite heavy-duty and I would imagine that things would not get loose over time.
The USB port is on the back and charging doesn't take an age. There are only two settings - on and off - and the light will run for 15 x hours before it starts to get dimmer and dimmer and then die.
Next up is the original Brompton battery light with build in reflector. This has been discontinued now but shop around and you can still find them. This is powered by 2 x AAA batteries and although it probably lasts as long as the 2C (if you use good batteries) it isn't as bright.
|The original Brompton rear batter light/reflector|
The final option is the Brompton Spanniga Solo - which is the current version of the rear battery light with built in reflector.
The version pictured below is the one I have on my Orange Flame Lacquer, powered by a front dynamo. The battery version is more or less identical in terms of size and looks but powered by 2 x AAA batteries.
This light has a horizontal strip of LEDs along the bottom of the light and it produces a good amount of light but I would have preferred the LEDs to be at the top instead.
In terms of cost:
Busch + Muller costs £22 - £25
Original Brompton light £15 (if you can find one)
Brompton Spanniga Solo £15
Out of these I like the 2C by Busch + Muller best. For me the USB charging is more convenient than batteries and the light is brighter and can be seen from further away. I also like the placement of the LEDs on the Busch + Muller light.
When it starts to get dark, I always have one of these types of lights with built in reflector on the rear (although mine are dynamo powered) and an additional flashing light. I think that the Brompton design is rather clever for being able to incorporate the light and reflector all in one without in any way interfering with the fold. If you only have the reflector these might be something to consider for convenience as much as anything else.
Stay safe out there people!!