I bought the cheaper of their two options- the Lumen 800, currently on offer for £55. It has arrived! I will update once I've tested it. I've turned it on and established it has four levels of brightness and that is about it so far.
Well, a quick test in the alleyway suggests that it'll do what I need it to do, might be a while before I get to test it on unlit roads in the dark.
The light unit is pretty compact- smaller than the Dinotte I owned years back. It clips on to the bars with one of two green O-rings supplied (for different bar thicknesses). The cable is long enough to give quite a few mounting options. Battery attaches to the bike with a velcro strap, feels quite a bit cheaper than the velcro strap on the Hope battery pack (which was elasticated so you could give it a good pull and get it on pretty tight)- but the Hope was in a different price range altogether.
The charger has a single (2-colour) LED indicator- it's easy to use, green to show there's power, red for charging, flashes when it's done. The light has one button, press for on, cycle through four brightness settings, just solid light- no flashing modes (good), hold down for off.
First impressions are good. Will post a picture at some point (just got a new phone and haven't got the right cable to hand)