We fitted our second one last night. Fitting the first one caused enough rows that Kofi Annan had to be brought in to mediate. Eventually we got it on and it works beautifully.
You'd think we knew what we were doing fitting the second ! (even Kofi wasn't taking our calls).
I now have a strategically placed wad of bubble wrap stuck to the pane with uv/weather resistant tape to stop it banging against the pane of glass. I fully expect to come home from work tonight finding a million bits of (toughened) glass all over the toms. The weight of the first one seemed to be enough to pull it off the glass. I think the triple spring in the second is that bit stronger that it won't "drop".
I have a well known make of greenhouse (Hall's), and these were a well known brand of auto vents (Bayliss). I shall be writing to both manufacturers and suggesting they talk to each other about getting the damn holes to even vaguely match.
(note to self: must remember to loosen the net shading over the new side to allow for expansion).
I'm sure they are wonderful inventions but they won't get the Nobel Peace prize from me this year.