I bought seven of these, and they are a great alternative to the expensive TM magazines. This is the company that fields the P90 to Echo 1, and they are the same mags, except they say P90 instead of E90 on the side. They even have the same typo, saying the round is a 5.7x2.8 instead of 28.
They do not go through Echo1's quality control, however. The mags are not afraid to split if overloaded. Three of them did this, four did not, but the problem is very easily remedied with a few drops of superglue on the problem area.
They feed every round, and so far have fit for me on a TM P90 and an Echo1 P90. I have not tried them on a CA sportline P90 though. No fitment issues, and take a load of abuse. I have not had the KS "loose round" problem in the KS magazines, though I am experiencing it with two of three of my echo1 magazines.
Good trades (not perfect, but look great)
Split when overloaded