So I’ve had my Raptor, Northstar, and Dark Magic II for a while, and only had to change my string every two or three days. Now that I’ve gotten my Catalyst and Avant Garde, after just a few hours, the string snaps. It doesn’t even seem to show any signs of wear. Is something wrong, or is it just my lack of experience?
Check the response area for burrs. There probably isn’t one, but it’s definitely worth checking for.
If you don’t find any, rub down the area all around the bearing and response with the rough side of a genuine leather belt for a solid 20 minutes on each side. It will smoothen out the anno, causing it to be less abrasive on the strings.
What type of strings do you use?
Just 100% poly.
Will that wear down he anno (by that I mean make the color go away, in case that isn’t clear)?
No, It will just take down on some of the roughness. Any difference will be extremely slight.
Don’t use cheap string.
This.
If you are frugal, at least use Kitty.
While cheap string is pretty poor in performance when compared to fancier string, cheap string shouldn’t be breaking, if you change it often enough.
But, you know, if you want some real quality string that won’t break, check out my sig 
I use the cheap string - generic slick 8 and slick 6 w/o problems. Rough surfaces will wear most any string. Rubbing down the anno will help. I’ve had to do that on a number of yoyos.
you could possibly have a bad group of string, but likly are just waring the string down. There may be a rough edge eating the string, but those yoyos have some huge gaps and if you throw strait down at the ground hard. You will be putting a ton of force on that string, where the tighter gapped yoyos you where useing before would just roll down the string rather then slam against the end of the string. I see this in kids I teach all the time, once they get super wide gapped yoyos they start killing strings at a much faster rate. Offten breaking them, sending the yoyo on a ride.
Check for imperfecting in the yoyo, but if you can’t find any then look at your throw, you don’t need to throw for max spin time each throw, just throw for the spin time you need for the trick you are going to do.
Then again it could be something totaly differnt but the reason I go there is because of the fact that it is those two yoyos you have problems with. Seems unlikly you would get two YYF A grade yoyos with string cutting issues. Not impossible but very unlikly.