No downers on the thumbhole stock whatever.
I've been using one on a walk & stalk rifle for big game, varmints and predators for over 30 years.
My LRH rifle has a thumb hole and my 338 RUM is about to.
The biggest plus is that if the thumb hole/pistol grip is properly fitted the trigger finger comes straight back under almost all conditions.
Also, I shoot everything single shot and notice no handicaps with the thumb hole.
I feel that the key to things is the 'fitting' of the thumb hole and pistol grip. Be careful material is much more difficult to put back than remove.:o
As was said above, personal preference plays a big part in the this.