I used to be on it (but I'm now on Symbicort). I got a substantial increase to my peak flow after I'd been using it regularly for a few days and a small increase straight away
It may make you feel a bit shaky, with a slightly faster heartbeat than you normally have but don't worry- that's pretty normal for ventolin. I have a tachycardia syndrome so I got a far higher heart rate increase (up to 210bpm during an asthma attack when I had to take several doses) than most get, that's why I was swapped to Symbicort.
We tried it this am, but went from 240 to 250:)