Rob pretty much nailed my experience with it in his post above. It is very finicky, and you need to learn how much to rotate it, being especially careful not to go too far, as it's nearly impossible to get 'back to where you started' in any reasonable period of time. I, too, color-coded the little arrow heads with different colored markers over a 'silver' Sharpie. Over time, your calibration mark 'moves' (due to cable stretch?), and I needed to be referencing a different mark after awhile.
As far as the brake lever is concerned, I absolutely have learned to use it to increase resistance for shorter periods of time. Also, if you accidentally move it's cable with your left hand, it will increase the resistance, annoyingly. Or, you could potentially view it as a 'feature' if you wish to slightly increase the resistance... 🙂
When I was initially troubleshooting all this last winter, I removed the water bottle holder to get a view of the mechanism underneath. It's basically a 'mixing unit', to which both the brake and resistance cables attach. Unfortunately, when either is made taut and then released back to where you started, the mechanism seems to refuse to return to that initial point. no amount of lubrication or fussing with it on my part would solve it, it's just a marginal design.
The 300PT is a great tool, however, and it changed my cycling life in ways that just about nothing else could have.
