I use the mezzo recommended cateye cube rear light on all my folders. On the Brommie and mezzo mounted on the rack it clears the folding and luggage areas. It has the advantage of being two self contained lights in one. Ie if one battery goes flat it still functions and you can have half of it on. I need to change the 2AA rechargables I use only about 1-2 a year tops. Only real issue is the batties are difficult to get out and I have to use long nose pillars!!!

If you go for the rollerblade option use clear rollerblade wheels (red cores if you can find them also). This improves safety as the lcd light is highly visable from the sides. If you use larger rollerblade wheels( 100mm+) the effect if quite dramatic ( dont have a picture)