I've had an occasional stuck bottle too, but the biggest problem I've found with the bench capper is that it's a flimsy scandal of a tool, and flexes so much that the caps are crooked.
I've read many having issues with the "cheapness" of the agata capper due to the plastic notch that sets the height, however I've not had any problems at all with it and have been using it for years.
Don't get me wrong, there's enough complaints to warrant an interest in its durability. But, I think there might be some user influenced problems. As I mentioned earlier, I found setting the height to just the right level is very important. You don't want the arm to be able to provide too much "over" leverage to the point where you are applying too much pressure without noticing it. I think in those situations the plastic notch piece would break or slip. As for unevenness, I'm not lying... I have not had a *single* bottle capped with my Super Agata bench capper (I think I got mine from LabelPeelers) come out with a bad or crooked seal - not a *single* bottle!, and I've done several hundreds of them with it.
Not trying to defend the product, I'm kegging now anyhow, just reporting my experience with it having been careful and taking the time to adjust it to where I found would be proper.
Rev.