It's one more thing to go wrong, not get torqued correctly, etc.
I've had two problems with mine this year. I have TJ to JK adapters in the front only because my Currie 44 is TJ width and bolt pattern. I have a Currie 60 rear that is JK width and bolt pattern. I'm running 37's with beadlocks, so need to run a 17" wheel. Chose to get the 60 with JK pattern because there's more wheels available.
So my problems this last year: When I got my tires mounted on my beadlocks, I had to get them balanced. The place that was recommended by Blaine canceled my appointment because they were too busy (just tires?). So I went to the closest place I could find because I didn't want to drive home with unbalanced tires. They snapped one lug nut on each side ruining both adapters, didn't even tell me they broke them, just let me drive away hoping I wouldn't notice. Luckily I put their job on a credit card, disputed it, they didn't get paid.
Went to another tire shop that was close to my house to balance again (didn't trust the first place) and see if they could fix the lug nuts on the adapters. They said they did, charged me for it (more than the cost of the balancing), let me drive away thinking everything was ok. Next time at Blaines, he noticed the lug nuts were loose on the adapters. Decided to replace the adapters at this point. I don't remember the full story from Blaine, but he mentioned that if I had gotten a flat on the trail, it would've been a bitch to get my wheel off. I would've slowed down my group which is not something I take lightly.
Plus almost every tire shop I've mentioned the adapters to gets nervous about them. Has to check with the manager if they're allowed to touch the vehicle, etc.
I've also heard other stories of tire shops breaking them, getting confused by them, or just flat out refusing to touch them.
Like I said before: Free wheels is not a good enough reason. If I didn't need them and you tried to pay me monthly to run them for some reason, I would not run them. I'd like to replace my front Currie 44 some day with a 60 and those damn adapters is the reason that bugs me the most.