What's the downside to Accu-rails?

I've heard some folks (even some very respected gunsmiths) say they don't like them, but haven't heard reasons on why, other than:

1. A traditionally fit frame and slide is just as good; and
2. A .22 conversion kit can't be used on an accu-railed frame.

Are there any other downsides?

If you don't care about the conversion kit aspect, it would seem to me, if an accu-railed gun is just as tight as a traditionally fit frame and slide, but has the added benefit of being easily tightened back up by putting on the next size larger rails, that's a pretty decent advantage (less down time and much less cost compared to shipping gun to a smith for welding and recutting rails on a loose gun).

Is there anything I'm missing?

It's permanent....you can't go back. If it's a dedicated single purpose gun, not sure it matters. This, like most other things BE that people like and dislike, is subjective.....Doug Jones is local here, and there are lots of folks that will attest to his work, acc-u-rail or otherwise. Plus his rates are very reasonable.

After this season I can’t wait to send my R1 out to him!

I had Doug Jones (Acc-u-rail) add them to my Springfield Range Officer .45 and fit two top-ends, one with rail on top for a red-dot and the other with iron sights so I can switch back and forth.  For the red-dot top end, he used a Caspian slide with Kart NM barrel and bushing -- the thing is freaking awesome.  Runs great and is stupid accurate.  I haven't ransom rested, but from sandbags it will put the rounds through the same hole at 25 yards, and by "same hole" I mean right on top of each other.  I'm very pleased with his work.  Total cost for all the work including building the new Caspian/red-dot top end was $1200.  Best money I spent on a gun.

As far as the 22 conversion, I just bought a Nelson conversion and spoke with Larry Nelson about the Acc-u-rails and the possibility of buying another conversion slide to modify for the Acc-u-rails.  Larry said that, while he would like to sell me another slide, he was confident that their conversion would work on the gun without modification.  He explained that the accuracy comes from locking the barrel to the frame and the slide doesn't contribute to accuracy, it only serves to feed rounds; he further stated that their top end will fit on an oversize Caspian gunsmith frame without modification and run fine.  I haven't gotten the conversion in yet so I can't confirm it, but I'll post when I get the unit.  I suggest you give Larry a call at his shop and get it straight from him.

I fully recommend the Acc-u-rails and Doug Jones' work.

I shoot a Pardini Sp and Hp so I don’t need a 22 conversion. I am definitely getting Doug to do some work on my 45