Hi S.!
We had this same decision to make not so long ago. First, can I ask why you are moving your 2yo out of his carseat? Not sure what kind you have for him but we have 4 little ones. 5,3, and 1 yo twins. We use the Britax marathon for all and just moved our then 4 1/2 yo out of the marathon to a booster. If you don't have to move him into a booster yet I wouldn't. If you have a Britax carseat that will surely hold him longer than 2 yo.
Back to your question... since we absolutely LOVE Britax we purchased the Regent but had to return it because it was HUGE!!!! We have a Honda Odyssey and it didn't not fit in the third row with the other marathon next to it. If it weren't for that we would have kept it. I loved the fact that it was a booster but still the 5pt harness. We ended up with the Britax booster instead.
I don't know of any other 5 pt boosters, but I haven't done the research.
Hope this helps a little!