Filing for the EIN is simple enough and I use it when I can, but some companies have forms that will not allow it and require a SSN. You can always tell the companies that you will supply it if your income gets to the required amount. Some require it to get started, however.
I think all of the companies listed in the getting started forums are legit, but there's always some danger if you put your SSN in their database. Their records could get stolen or hacked, or they could have a corrupt employee.
So far (knock on wood), I have not had any problems with my SSN being on file and I think I'm registered with just about every company out there.