I have a DS at Yavneh in Y8 and he's very happy indeed. He's also thriving academically - with 5s and 6s in most subjects (from a base of 4s and 5s at the end of primary) with end of KS3 targets of 6s and 7s. To be fair, though, friends of mine with children in middle or lower sets complain that their children don't get the best teachers, that these are kept for the top sets. It's difficult to judge this. My DS is himself in a couple of middle sets and hasn't made this complaint; however he's eager to move up due to the curriculum being "boring" (his words) in the middle sets.
Since my DS isn't sporty, I don't know much, but there's lots of provision and a great keenness amongst the staff to encourage this side of things. There are school and after school activities in all sorts of sports.
It is true the school is strict but don't believe all you hear about being locked all day in isolation rooms. We have had - it is true - quibbles about group punishments (shorter break) for a class where a few kids have been noisy, but in general, if your child is well behaved, they won't be bothered by this. The uniform policy is also seemingly very strict but again, this masks a lot of flexibility, especially when the children first start. On the plus side there's a system of credits which means the children get lots of encouragement to behave well and most do. However, like all comprehensives there will be all sorts in the school.
For an academic child it's a wonderful school. The teaching is excellent and even in subjects my DS doesn't enjoy, they've managed to enthuse him. He's also made some wonderful friends: the lunchtime enrichments (like after school clubs, but 40 minutes mid-day) mean that children get a chance to meet children from other classes and other years in varied topics from chess, latin and radio broadcasting to movie reviews and 'history of Borehamwood'.
Lunch itself is a bugbear. The cafeteria is small and (as far as I can tell) not well organised. The children complain about unappetising food and that it is frequently cold.
I'd strongly recommend the school. If comparing to JFS, remember also that it's half the size when at full capacity: a great strength in my opinion.