Basically, if you aren't port forwarded, you will get less peers. This is because you aren't allowing incoming traffic, so only other port forwarded peers can talk to you. If you are port forwarded, you get all the peers.
With vpns that support port forwarding, you can set the port forwarded port on the VPN to the port in your bittorrent client and it will allow incoming traffic.
If you need to hide your torrenting activity, just use a seedbox
I never understood seedboxes. A VPN on my own hardware works nicely. I hate cloud stuff. With a seedbox I'd have limited storage and would need to constantly pay monthly fees for it. Instead, I can just use my own hard drives on my own hardware.
Terry*