We sell a business tool, once the business account is upgraded, the rest of it just pay per seat linked to that org. All our sales are done over the phone, so we don't need to accept payments in app. We never ever tell you in the app how you can upgrade to the premium version. We never even link to our own damn website out of fear of Apple's wrath.
About 1/4 of the times we submit big fixes or feature updates we lose the game of Apple Review Roulette, and get denied. So we have to do an appeal and explain it all, again, and so far at least, the 2nd tier always approves it.
Practically, it just means that everything we do with Apple, you have to plan for it to take 2 weeks
It is so much faster now.
Not only that, there is always the chance that 2nd tier support will stop approving your app and then your users will be stuck with a version of the app that needs bug fixes that Apple won't allow to ship.
You release version v1.0, with something that's borderline under Apple's policies. Apple approves it.
You release version v1.1, with just bug fixes. Apple decides what you did in 1.0 wasn't OK after all, so you can't release your bug fix until you're removed whatever apple thinks is noncompliant.
This happened with Hey, for example.