The 10% for who it is not can add or correct things that our IRS may not know correctly (i.e. foreign holdings or bitcoins).
You then digitally sign and submit it. It's quite easy to do yourself and I think most people here do (couldn't find a percentage). I could find that 97% is submitted digitally, only 3% is on paper.
We do have commercial offerings, those are used for the more complex scenario's, mostly by accountants and tax professionals