New GS'er in London. Need some advice for "city" GPS

Looking for some quick info. I'm going to pick up either a Tom Tom Rider 400 or a Garmin 390LM this week since navigation is my enemy at the moment... I've seen a lot of info about how great these things are in Europe, the twistys, etc... anyone have experience around London?

I'm on a new-to-me '04 GS 1150 Adv and will probably just mount it to the bars for now. so i suppose not having to perform open heart surgery on the wiring would be nice as well if you've got a read on that.

Thanks in advance.

Either will do the job; I have a personal preference for Garmin, but others favour TT, buy from somewhere that sells both and compare graphics, menus etc. As to mounting it, the optimum solution for your bike is a Migsel mount that mounts around your speedo and presents the unit just below your eyeline. Wire it direct to the battery with a fuse on the +ive, or via a switched live, of which there are plenty on the 1150, the easiest to get to is the pilot bulb which is always on with ignition.
Any GPS will struggle around tall buildings as it needs to see the sky, but once you accept that limitation it's down to personal choice.