OK, I have a jaded view of Abacus. Or rather, I have a jaded view of any 'maths scheme' from which a teacher teacher 'pre-planned' lessons and the class then does 'pre-set' exercises.
My son is very able at Maths (he could add and subtract negative numbers in reception for example). However, because his school - which I am otherwise happy with - uses a maths scheme, he sits through lesson after lesson in which he leanrs nothing new - because the teacher, even if she is aware of his ability, cannot start the lesson for him at the correct point because it's 'not in the scheme' (I know there is a challenge book - buit the mechanics of teaching wholly separate 'challenge' lessons don't sem to work out).
Equally, most of the exercises are 'reinforcement' for him - but he still has to wade though what seems to me an unreasonable number of repetitive examples before he can get onto the explore questions. And his current teacher is of the 'underline 3 times and write only in boxes' type and so cannot understand how my 'bright but scatty' son is using up almst all of his time doing these repetitive sums but straining every sinew to do them neatly enough to satisfy her.
The half termly tests seem to, in my sons's school at least, replace proper continuous teacher assessment and are taken as 'gospel' .
I compare this to the maths planning I do - from the framework, starting precisely at the right point for each of the groups, with appropriately differentiated activities for each group starting at the right point, with no need for top groups to wade through easier activities, with conitnuous teacher assessment and I grit my teeth VERY hard!
Obviously, there are ways and ways to implement and use a scheme. Used selectively and sensitively, they are probably fine, and they may well be fine for your 'average performer' ... it's just used verbatim for someone who has the capability to be an exceptionally good mathematician if encouraged is a bit grrrrrrrrr