I'm also hoping that their manufacturing process is better than ePBT. I've not had much luck recently with ePBT/Gateron caps. Lots of shrinkage leading to banana-shaped modifiers that will only work with costar stabilizers and VERY tightly fitting caps. Like, "scared you're going to rip your switches apart" tight
That sucks to hear, where did you get those sets from? I've gotten 4 sets of ePBT caps from KBDfans & none of them have the warping issues on spacebars or modifier keys, I use them across a bunch of different boards without issue. Not sure if I'm extremely lucky, KBDfans has real good ePBT sets, or if that is just the exception & not the rule with ePBT sets, but you are not the first person I've heard of having this issue with ePBT or Gateron sets. With my personal experience with ePBT though, I'm leaning more to that being the exception rather than the rule.
I've heard of people using a heat gun to get bows out of longer PBT caps though, might be worth looking into if you haven't returned the sets. The stems being tight is something that my sets do have though, I believe it's because they are made for Gateron switches which have a ever so slightly smaller stem than most other MX switches. Although I don't find them to be so tight it worries me removing them even on Cherry switches. I'm all for a higher quality product, hence my interests in this GB, but IME ePBT is pretty good as it stands. I'm expecting better dye-subbing with these BSP sets but that's about it TBH.