I emailed with the owner of New Company and spoke on the phone with the owner of Old Company for about an hour this evening. Both of them feel comfortable with how they do business to comply with all of the federal credit protection laws. This FTC action seems to be more of an incitement on how this credit repair company was offering specific promises and not delivering based on their deceptive practices.
Neither of the tradeline companies recommended are credit repair companies, nor do they promise or guarantee that a person's credit will go up, or how much. Old company sent me a copy of their agreement with authorized users which notes in the caveats, representations, and warranties section that they "do not and cannot guarantee any specific result or specific increase in credit score."
They do offer a refund if a tradeline doesn't post, as Car Jack mentioned, but they don't offer any promises about what that line will do for one's credit score. The owner of old company indicated they as a company had no complaints that he was aware of with the FTC, BBB, CFPB, etc.
The above company in question clearly did--they were scamming people out of millions by promising things and not delivering, and those people complained, with good reason. That doesn't appear to be the case with either of the TL companies I've used, and that's good.
And, of course, even in the above case where the credit repair company was (allegedly) fraudulently misrepresenting themselves, it doesn't appear that any cardholder of their tradelines were caught up in any sort of issue with it (other than perhaps they didn't get paid when the company's assets got frozen).
I do note that there are other TL companies I've looked into who didn't meet my criteria for one reason or another, but do various "credit repair" besides tradeline sales, which might open them up to some of these type of issues, so it's good to be wary of that.
The FTC in this case is protecting consumers from the scam this company was doing. If they wanted tradeline sales to be illegal, or removed from practice, they could do so (and again, the last time it came up before congress during the FICO 08 thing, the FTC was on the side of forcing the credit bureaus to keep the practice of authorized users allowing credit score improvements). If I was worried about the legality, I wouldn't participate personally.
So overall, I am not concerned or plan to change my behavior regarding tradeline sales. As always, do your own due diligence, consult whatever legal advisors you feel appropriate (I am not a lawyer, just sharing my uneducated opinion and personal plans), etc.