My DS has done the long papers from Learning Labs and found the maths and codes fine. He struggled at times on the English but then that would be his weakest area (word knowledge). I think that they are of good quality and I would rate them quite hard in places possibily between Daughtry (Bright Sparks) and Walsh. My DS is getting between 80-90% on most papers with maybe one paper slightly over the 90%.
We have not done Learning Together so I cannot comment. Walsh is deemed the hardest of the shop bought papers with Bright Sparks behind that. The Tutors L4 is ok, maths and codes wise, but hellish on the English. I have to confess there have been times I had to look words up myself (and I am guessing I am not alone here!
) I am using them just as additional practice and not stressing if DS2 looks baffled. DS1 also did these papers and was hitting 17-18/20, which is considered very good. So if your DS is scoring well in most tests he is getting a good prep