Few times I accidentally logged on to Bitsler using VPN, received only email to confirm the new IP address and use them without any problem. I think the probability two users to use same IP from VPN is very low, and there is no overriding reason to worry if you do not do illegal activities.
This is indeed a very small chance that the same ip is going to be used by the difference person but like I said before that it has the chance. Even if you do not do the illegal activities, some might do it so if you are using the same ip as them then Bitsler is going to think that you are the one who did it, because it is untraceable. And btw the same ip can be used more than 2 people right? So the chance will increase draatically if many free vpn users out there, unless Bitsler authorities can guarantee this