VPN's designed to work around blocks utilize a variety of masking techniques. The problem with cafe or other place, they could have a UTM doing DPI and Application Layer Inspection. It's going to recognize the TCP snippets from the VPN client in most cases.
However some VPN providers even try to get around this. Switching to TCP and utilizing 443 can trick some. Some allow you to specify custom powers, and throw TCP traffic over Port 53 (DNS) bypassing filtration because a lot of IT guys don't filter DNS.
In many cases, it's a matter of trial and error to get something to work.