Since I was curios and they’re pretty cheap, I decided to get an MT300N-V2 to test its VPN speed.
So through a wired connection (and using Private Internet Access as VPN provider) I get:
MT300A: 1.31 MB/s peak, ~10.5 Mbit/s
MT300N-V2: 1.34 MB/s peak, ~10.7 Mbit/s
Firmware version was 2.264 on both.
So surprisingly, the MT300N-V2 is at least as fast as the MT300A. Still slow, mind you - but now it would be really interesting to see how the performance would be if the hardware acceleration was being used.