There are rules about who can REGISTER using VPN, and how. Once you have your account, you can use a VPN, it is in fact encouraged on the Rules&Info page:
My privacy is essential to me. Do you have any tips for me?
- Don't post personal information (name, address, phone, email, pictures, etc).
- Use a unique username for every website you use.
- Use a proxy/VPN once you are registered.
- Tweak your preferences and privacy options to your liking here.
- Use a secure or disposable email provider