Well I decided to join the club after seeing the N5100, 4x i225 box on aliexpress for $113.
I've been wanting to build a pfsense box for a while and couldn't pass up the deal. Really glad I found this thread and all the good info
https://www.aliexpress.us/item/3256804116114245.html
Fortunately I have a bunch of copper shims already, since it appears this WooYi version suffers from the cooler gap.
I'm surprised how little info there is on the N5100 version specifically, but I will update when it gets here. It seems like the N5100 might be the better option for minimal power draw, compared to the N5105. TDP is 6W vs 10W, base clock is 1.1GHz vs 2.0GHz, and turbo is 2.8 vs 2.9, so I wouldn't expect much difference in max performance, but hopefully it can save a couple watts in normal use.