This may not be what you are experiencing, but my low point drains just spun around and didn't seem to do anything. I finally figured out that they pull up to open and push down to close. Might want to try pulling and pushing before you remove the valve.
If you need to replace I would use something like a diagonal cutter (dikes) pliers to remove the crimped bands. You can usually rent or buy the pex crimp tool at home improvement stores. You might also be able to use a SharkBite but since they use something like an o ring to seal I would be concerned about the groove left behind by the crimp band.
But the SharkBite might be long enough that you have to trim back the pex and then it will all be good. As far as ease of use, if you can push a straw into your Big Gulp you can push a SharkBite fitting onto a piece of pex. It's really that easy to use.
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