Brompton Rear Light

I got a Lezyne Laser light which is a shorter (vertically) but wider light and veryh bright on thee highest setting. It has something like 15 settings what with flashing, solid, different flashing patterns, strengths, etc. Probably a lot more if you double it up with laser lights on and off. Those are dashed red light lines a bit outside of the bike width to demarcate the space you should own on the road. IIRC 0.5m out on each side. I think they kind of move forwards and backwards too so the motion makes it noticeable more.

Plus I only have to charge it practically once every two months (15 or 20 minutes each way on the work commute leg and a couple more minutes on thee home leg. Not long each day and 3 days a week means it lasts so long that I kind of not remember when it was last reecharged. IIRC when I commuted 35 minutes each way in my old job it lasted 2 weeks if I risked it but I tended to charge it sooner than that.

The other decent design feature is a short press of the on/off button and a small light comes on in the face at the top. This shows green, amber or red according to how much charge is left then it goes off after a couple of seconds. This gets around the fear of charge running out mid commute and the wasteful mid battery recharge to be certain.

Lezyne IMHO make very good rear lights so the one in the OPs post or my Lezyne Laserlight are both good Brompton fit and leave on rear lights.

Rockbros Q5 light with the mount that fits on the saddle rails. Have 2 in use and I love them. Doesn’t twist left or right like one with a rubber strap. Looks and feels fantastic due to it being very well made. Turns on automatically in the dark with movement and has a brake light function due to a sensor. Rechargable via usb-c (old one micro-usb and still in use on mine) and the charge lasts a pretty long time.
Best of it, cheap via some well known channels. The not so good, not as bright as some as the crazy lights out there and be careful wearing a jacket as it might cover the light.