Expats generally can’t purchase “A” shares. “A” shares are those denominated in RMB and “B” shares are US$ denominated.
I’m not sure if the “boom” you are thinking about still exists.
Mutual funds are relatively safe, though their growth is not as strong as it once was. There was a long period when I’d get 20% a month on a mutual find, but now it’s generally more like 2% — still better than the bank, though, but you need to pick carefully.