The belt does stay tight after it slips over a tooth. Once, it popped off. Each time I try putting it back into place it slips right out of place as soon as I start it.
On a side note, the offbrand tensioner is considerably cheaper. I'm not making much money with the machine right now...
I replaced a drive belt this spring due to it shredding last year. Shortly after replacing, I noticed it slip over a cog(?) on the pump pully.
I'm going to replace the tensioner, because I'm pretty sure thats the cause, but I couldn't find any sources citing a tensioner causing 'tracking'...