Edit: I currently see 279 supporters for a total of $2,328 per month, so $8.34 average per month per supporter.
The pre-populated options are $20 and $100 a month, which is a lot. I think he'd get a lot more supporters if he dropped those asks to more like $1 and $5.
Either way, $5 is probably both the median and the mode for the payment distribution, whether you include non-paying members or not.
From memory I stopped because I was adding other creators and I got the impression he was doing okay.
Edit: I currently see 279 supporters for a total of $2,328 per month, so $8.34 average per month per supporter.