I see no reason why not.
While I haven't tried any of the aftermarket holsters out there with mine, I see little reason why they wouldn't work.
The Hi-caps are just as accurate as any other Makarov out there...the only flaws are typically in the finish. The commercial russians don't quite seem to have the care/finesse put into them that many of the others out there do.
Also, the factory adjustable sight is a little sharp and likes to snag on your clothes...Makarov.com used to have a replacement fixed sight for this very reason (I have one, and it is SWEET!) No longer available, but there are companies out there that could make you a custom sight if you desired.
The only other issue would be magazines. For the most parts, the original 10/12 rounders are just fine...most of the problems come from the Pro-Mag magazines. My biggest problems with the Pro-Mags have been poor construction (They don't take long before they start developing cracks around the feed lips) and the springs are a little on the weak side.
2 of my 3 Pro-Mag magazines won't reliably feed steel-cased rounds...for whatever reason, they hang up after 2-3 rounds. Brass cased rounds seem to work find. They all seem to work fine in the original mags I've tried.
From what I've heard, th Pierce grip is the same width for the Hi-Cap as it is the single stack makarov...so if you had both with the pierce grip, they would feel the same in your hand. BUT...the single stack makarovs with other grips will be thinner--which is more easily concealed.
For plinking/target work, I enjoy the wider grip. I even put a hogue slip-on grip on mine. Feels great in my hands!
I love my IJ70-18AH.
