I have used them before and they are fine. They're all pretty much the same.
Here's my challenge to you... why do you need it? In this era, most people have free calling on their cell phones... but using this service creates a tangible cost to you where none may need to exist. Nobody really thinks twice about calling a regular phone # any more.
I don't want an 800#. When ever possible, I want people to communicate electronically, but they absolutely can call us on our regular phone lines.
If you do need an 800# forwarding service, I have used a few and can't really remember which ones but never had any issues. You can easily find what you are looking for... just don't be too quick to add operating expenses to your side of the ledger books.