If you walk into a sign store they might have it. It’s a specialty item, so online is often the best way to get a good deal.
Depends on your use case.
It tends to be really sticky, and may adhere a bit too well to your material. Too sticky could lead to pulling up wood fibers, or being punishingly difficult to remove. Also, blue tape sets up in about 3 days, so don’t leave it on or it’ll probably grab your material so hard that you’d wish you never used it. That being said, it can be used in a pinch, though the widest I’ve ever found it in store is about 3", so it’s kind of a pain to work with.
As for:
Sandpaper takes that right off. Test the cuts to find out what the minimum power you need is, and then just sand your pieces briefly at like 400 grit, good as new. I rarely mask hardwood projects if they’re larger pieces [like boxes or trays, etc], I’m going to be sanding the project anyway.
My test method:
If you overpower your cuts you’ll get much worse flashback, and then masking or a sacrificial layer of cardstock underneath the part will probably be needed to protect the back surface. You generally want to cut at the fastest hottest speed you can get reliable cuts with, and most flashback issues go away.