Yes, I ran the London Ultra as my first ultra. It was fun! Rather more on road than the other runs suggested, and less hilly than most of them. It's mostly well signposted. If you decide to run it, let me know and I can give you extra details regarding the bits that are not so well signposted - mainly some bits into and just after Wimbledon Park, and as you enter Richmond Park, also to watch out for the slight deviation from the published (non-race) route for crossing the Thames. And apparently there's a large footbridge over the big road just before Richmond Park, which you can use to avoid the 4-5 mins wait to cross the road at the lights. I recced that part of the route twice, I think, and ran the race, and never noticed it...
Got a huge mug for finishing - made a nice change from a T-shirt.