No, because i don't own any
IF i did, i would consider 3 a touch much, and 9 an invitation to have someone boot me in the nads.
Really it depends on who you play against. If your local meta likes hardcore gaming, bring 3, or more.
If you are looking for pickup games, write some lists that have 1 or 2 vendettas instead of the 3 (or 9, or 18...) that always seem to fill
IG lists... or even a few lists that don't use them (for variety). I understand wanting to use the models you've lovingly assembled/painted, believe me
Other armies:
Purifiers i'm less than fond of, as i run hordey orks a lot... Against Marines they are so so, against ork mobs they are beyond lethal.
Same goes for blenderdreads for
BA.. nasty things.
Neither is utterly beyond the pale, just unfun to fight.
The main problem with the Vendetta isn't so much it's rules as it's grotesquely low price. The Ork Blitza Bomma is spendier, can't be squadroned, has worse
BS, worse guns, isn't VTOL, has worse armour... you get the idea.
Same goes with other vehicles too, just using that one as an example. If the Vendetta was say 180 pts it wouldn't be complained about as much, though by rights it's combo of armour, guns and other goodies should clock it over 200
If you want to run 'em, run 'em. Just realise that other folk may consider them unfairly cheap.