True.
There are a lot of unknowns. Even if I was an established developer, I would find it hard to accept that Unity will be informing me how much I owe them based on data they are not willing to share with me. If I was getting a bill for installs, I would want to understand specifically how that number was established. Without that knowledge, the developers are having to "trust" what Unity is telling them.
There is also the issue with Early access and what constitutes a new install that would be charged. When A21 dropped, I installed it. I also went back to A20 and A19, then returned back to A21. If those are each considered a new install, that would be 4 installs. At the highest rate level for Unity Pro, that would be an expense of $0.60 for TFP (using the highest rate just as an example). Even though $0.60 is nothing (I got that loose change in my car), for me it becomes more principle than the actual expense.
Throw in the fact that some people are not very trusting of the Unity CEO and some of the things he has said in the past, people are going to assume the worst about this rollout, especially since it was not very clear when it was released in the public space (might have been a better rollout to the developers internally).
I think we will be seeing more information come out after the initial rollout was bungled. I am hoping Unity proves me wrong on some of my thoughts, though I am not a game developer so it is mostly just curiosity on my part than anything else.