many people now here could answer to this question.
Basically, I buy a subscription like any users can do.
Then I use Firefox Portable to set a private proxy. in that way, we all use the same IP.
The saas or website has login prefilled by me.
If people tries to change something in the account info or change the password, the account blocks and then I have to reset password and everyone in the group buy are waiting about the new password.
After buy the GB from me, you will receive a zip file, you just have to extract the folder in your drive and use the firefox.exe.
you can now use nicely tool for a very cheap price