For our clients, the appeal of Mandrill is the Mailchimp Template Editor. I think this is where their focus is going and so if you don't need that, then definitely check out competitors.
> I will purposely challenge their solution to see how they react.
> If they get defensive, it’s an immediate no-go. Remember, there’s a difference between defending which is good and being defensive which is bad. The difference is that the former is based on rational facts, the other is based on emotion.
Are you always able to challenge them based on "facts", or are you going to challenge them with your current world view? I can see someone getting defensive if your challenge is perceived as deliberately provoking.
Surely, if PwC is wrong, and Patreon is responsible (which seems this way) and HMRC decides to investigate, they will go after Patreon, and not individual users?