I've never had a problem (other than it's initial outing when it was settling in) with my AR47 build. I use C-Products and ASC mags exclusively. I have three other AR47 owned by family and friends and they have had no problems with theirs. I have about 700-800 rounds through mine and the only issues were within the first 10 rounds, after everything settled in it's been flawless. I've shot 7-8 different types cheap steal case through it (wolf fmj and hp, golden tiger fmj, tula fmj and hp, fiocchi brass case fmj, red army hp).
In regards to the weird mags, the 28 rounders fit in standard STANAG mag pouches so aren't that far off. They do have more of a pronounced curve to them as compared to STANAG mags. The 30 rounders I avoid simply because they don't fit in mag pouches. But more often then not I use 20 or 10 rounders just like my AR15, as I like the length and that it doesn't get below the grip. The 28 rounders look very similar to 6.8 SPC, or 6.5 Grendel mags, but people don't think those are "weird".
I've said in several other threads the key things to know about assembling/buying an AR47:
1. Enhanced Firing Pin
2. Actual 7.62x39 Bolt, not a 5.56 bolt milled out, buy a quality Carpenter or 9310 MPI bolt
3. CProducts or ASC Magazines
4. Buy a barrel from a manufacturer who knows what they are doing on the feed ramps for 7.62x39, most have this figured out by now if it's a reputable company
5. I prefer carbine gas for an AR47 just to ensure reliable extraction on steel case ammo.
6. I run an H2 buffer in mine and it works well.