Yes I understand that, the internal and external dimensions of the four brands are identical on the pipe so can be fitted to different fittings with the right crimper for the fittings. May not be to the code but they do fit, similar to the different polybute water pipe systems around. Not saying do it,  just that it is possible if no other choice is to hand at the time. Was told this by the Kembla rep originally, checked at a supplier and yes they do all fit.

Yes, when there is a problem everyone ducks for cover. I don't mix brands but think the regs are still playing catch up with the new technology of composite pipes. Mixing copper and galv from different manufactures doesn't seem to worry people if they conform to the relevant standard, why not composite systems that are made to the same standard as long as the crimp tools used are designed for that particular fitting. Who hasn't mixed polybute systems when doing alterations ?
Just my two cents worth, aren't the regs also open to  "acceptable solutions "?