Long time user here. I only use them to test fire my markers after tear down/rebuilds in my home. So, really not more than 20 shots through any marker with them at a time. They are a great tech-gadget IMO.
1) They bounce like crazy, so use something tough + soft to hit. I use a pillow or two under two 'scrunched up' blankets. Blankets may be ripped through if you are using full auto due to repeated quick hits in the same location.
2) MAKE SURE YOU CLEAN THEM! And by that I mean dust them off, remove any grit or hair that they accumulated wherever they land. That stuff doesn't go well with internals of your gun.
3) They are a smaller bore than regular paint, so I feel they shoot slower than regular paint, but not sure. I will confirm with my radar-chron after a day of play + tear down on Sunday.
4) THEY HURT LIKE A B! Or so i've been told... with more mass they could potentially inflict more damage even at a lower FPS. Add to that when i'm using them its indoors to test, so it's really close-range. DON'T, EVEN FOR JOKES, SHOOT SOMEONE WITH THESE AT CLOSE RANGE. not nice.