Has anyone used one of these?  I have a G35 that I'd like to turn into a "G34" either by another slide and factory barrel or BAR-STO barrel.

Thanks

I am in the process of trying to do exctly that with a KKM. I have tested it with all stock parts except the barrel, and mags of course, and have had two failures to extract. Both the same and both in the middle of the mag. My next test is to put in the 9mm extractor to see if that solves the problem. The stock ejector seems to be working just fine though.

I never even thought about getting a 34 slide and the factory barrel.

I did the barsto 9mm conversion to a G23.  I just had to do some minor sanding to get the fit, and its worked great (1000 rds or so) - zero issues.  Barrel swap & 9mm mags, no other mods.