I have a stackmat timer (because I got if for Christmas years ago when I was into speedstacking). It's pretty durable, doesn't glitch often, and overall works well (and it's a 1st version timer, which could be what you are getting). On the other hand, I have used and seen QJs that are breaking and and can glitch more often.
If you want quality, and don't mind a higher price, I would suggest going with the stackmat.