Hi Nick
At a guess in the NEFTA winter league it's about 3/4 red dot, 1/4 scopes. Taco hold isn't allowed though; arms' length only. I believe pistol HFT in the UKAHFT has an open class to allow taco holds and a traditional class for arms' length.
It's whatever you get on with best. Pistol scopes are like marmite. I started using a Bushnell Elite 2-6x32 which was a beautiful little scope but in the end I found I got on better with the holographic red dot. JSR do a very good 2.5x32 long eye relief pistol scope for £not-a-lot. I've looked through a couple of these at the club and they really are very good for the money. I'd say the safest choice is a quality red dot with a small dot size for precision.
“We are too much accustomed to attribute to a single cause that which is the product of several, and the majority of our controversies come from that.” - Marcus Aurelius