I have had a lot of them done. On a 686 there is a difference in the different dash numbers, so let him know which one you have and get the proper moonclips. The work done by TK is first rate and the mod is a good one to do if you shoot or plan to shoot any ICORE or USPSA matches. You will still be able to use your gun with out moonclips.. I recomend it.
Tom converted a .38 Special Model 642 cylinder to 9mm moonclips for me. Turnaround time was 7 days from the time I mailed it off until I got it back. 9mm revolvers have been known to have extraction problems due to rough cylinders, but this one has chambers that are as smooth as glass, and I haven't had a single problem. I highly recommend TK Custom.
I just sent my 686 SSR to TK a couple of weeks ago. Turnaround was less than a week. Tom is a nice guy who answered all of my newbie questions by phone. He does fantasic work and was cheaper than anyone else for a couple of reasons ... his price includes return shipping and chamfering the cylinders holes. Also cuts his own moon clips on his EDM machine.
There are no downsides to moon clips. Well maybe one ... when your reload times still suck, you have no excuse.
Moon clip conversion and the BMT mooner is a slick setup. I got the BMT last week. BMT Equipped, Inc.
So far, TK Custom has machine three 686's and all were excellent work. Fast turnaround time, too.
Personally I like the moonclips a lot. Sometimes when hiking I even carry them in one of those pouch that splits the seven rounds over my belt -- four on one side, three on the other. So far they've worked just fine.