It really depends on how you interpret the guidelines of Pixiv: https://www.pixiv.net/terms/?page=guideline&lang=en.
My problem is that I can't be staking my living on the whims of the site (e.g. Patreon) and the interpretation of its rules. I chose SubscribeStar because it's the most reassuring thus far.
If you've seen similar content to REC where the author used a SubscribeStar alternative, I'm always down to take a look too!