SchoolBooking seemed great in terms of features & cost until we had to stop the trial because a MAT decision was made to move to Bromcom.
However, I know that other schools in the MAT had SchoolBooking established well before the change-of-MIS and that they are still using it after the migration was completed.
I'd imagine all they did was change the Assembly Connector (SchoolBooking's chosen MIS sync application) to point to Bromcom instead of SIMS.
There was also SchoolCloud but that turned out to be more expensive than SchoolBooking for (what I remember) no real difference other than it looked more modern.
Taking a quick look at their website again, it seems that they don't even support Bromcom anyway.