I'm also using the WAS groupon stick with a huge fan on it. I really wish they would build a proper fan and cooling duct into the stick and power it with the stick itself. It very much seems like a half-assed solution.
I'm considering that and the Nokia G-010S-A on my Uni-Fi Dream Router 7 (my area is serviced by multiple wholesale network access providers who operate either over GPON or XGS-PON, hence the need for both). However, I've heard enough horror stories that I'm a bit concerned about temperature issues...
all XGS models I've tried run super hot. I don't know the standard for your area but here 99% of the time here you just get a 'media converter' style layer 2 ONT which I would just keep.
https://www.fs.com/c/gpon-xgspon-sticks-5607 (I think this is what you're looking for?)