I started going to Ten Pilates on weekends and have been really enjoying it. I am a complete beginner but the classes are not too crowded and the instructors are very good and take the time to give you some personal advice. If you buy a pack of classes its pretty cost effective too.
The location itself is super convenient and very central in an area (St. James's) where there are not that many Pilates options. The only downside is that its in a basement and has no natural light. That being said, they have done a great job with the space and it feels clean and airy.
All said, I would definitely recommend.