I work in the office at a secondary school in South Yorkshire and we were looking at an MIS change at the start of the year, ended up putting it off because of Covid (ironic really, my job would have been far easier without sims).
However we'd looked at both Bromcom and Arbor and there was similar feedback with people saying it appeared to be more primary focused.. I'm not sure why really. I would agree that it perhaps looks a bit simpler, but surely this is a good thing, why make it over complicated?
I can't comment on assessment as it's not my remit, but I do recall Arbor are now working with quite a lot of secondary schools, and as the link above suggests a very large trust with several secondary schools.. If the really important bits weren't up to scratch then surely they wouldn't have being awarded that tender in the first place?
I also think that suing an educational institute just isn't cricket, more so because from what I've read they haven't got a justified argument really. This alone would be a big deciding factor for me, they should behave with a bit more decorum