I think you would be fine, but if you sign up and if they want to then yea they can sell your number, etc to people and you could get spammed.
But...
if you really want to do this, then use Spoofapp! It IS ssafe to use and has been talked about on the news, etc and you are sure to be safe and not spammed if you use their service!
And these apps don't spoof/fake the caller ID words! They just spoof/fake the number, not the word part! And the number needs to be 10 digits in length... no less, no more.
If you have any further questions about this subject, then please ask?