There is nothing wrong with the Keycool POM set. Seeing as how you are aware that the fitment will be tight, you just have to act accordingly. That Keycool POM set is on a board with MX Clears. If you have encountered how MX Clear stems are, they can be a total pain in the ass especially with brand new key caps. If you think the POM set will be tough to get on and take off, try putting them on an MX Clear stem. I knew full well what I was about to get myself into. I used a cotton swab to put a
touch of Superlube (the thing that came to my view on my desk as I was lubing some switches at the time and thought it wouldn't hurt to try) on the inside of the keycap. Just enough of a light coat that when it came into contact with the switch stem, there would be no excess seeping out. I then took a pair of pliers which held a Clear stem out of its housing and inserted and removed the keycap about 2-3 times. It was a complete pain, but it worked. It still requires some effort, but as long as you don't mindlessly pull with your keycap puller, the keycaps come off nicely.
It was the first time I've tried POM keycaps and I couldn't be happier. I doubt I'll be swapping keycaps on the 660M any time soon. You've already been informed to be cautious, it's what you do with that information to allow you to carry on. Don't let people's mishaps such as the tight fitment on DSA keycaps or the ones that blindly placed the Keycool keycap sets on their keyboards and later on finding out they removed the stem from the housing once they pulled the cap off to go in vain.