People have used them in FT for many years.
B***er ... read the title before posting.
Er ... HFT ... Weight will be further back and, in my opinion, better balanced ( especially for smaller shooters ), on standers and kneelers.
Yes the scopes may be higher. You just learn your aim points.
This can be an advantage, not a disadvantage, if the shooter is not great at ranging at longer HFT ranges, but very good at sub 25 ranges. The high mounts, and bore to scope distance, mean the aim points are closer together at the longer ranges. So you may get the distance wrong between 40 and 45 yard targets and still knock them down.
The payback, as Tugg says, is there is more holdover at sub 20 yard targets. That's ok if you are good at ranging close distances. You just learn your aimpoints at the closer distances.
I shot HFT with high mounts. Once I'd learned the aim points it's fine. I had a 35 yard zero and my close zero was around 17/18 yards. Below 17 yards the holdover obviously gets bigger and bigger ... but once you've learned the aimpoints, and I found ranging below 20 yards easy, it's no problem.
Some won't like it as there are 15mm kills down to 13 yards and they like to set up the kit so you can aim bang on for all 15mm kills. You only get 15mm kills prone. So, once you've learned to range accurately below 20 yards, you shouldn't have a problem aiming and hitting 15mm, HFT prone, under 20 yards. You still don't have to range them within a yard. You can be slightly out. At these close distances, HFT prone, you should be getting just ragged hole size groups. So you do have some room for error, even with a 15mm kill.
To be honest, and I'd have to check ( not shot HFT for a long time ), but I don't think I was out of the kill on 15mm, even at 13 yards ( top of kill ), so it's not that big of a problem. Below 13 yards and the kills are 20mm minimum. You miss 20mm under 13 yards because you don't know the aim points of your kit or you can't see them. If you know your aim points and you can see them and you are missing 20mm, HFT prone, at 12 yards and under ... do something else.