3M Photo Mount rocks. I also use brads and eyelets a lot. The vellum glue dots have completely failed on me, I have some pages that I have to reglue some things on
Do they 'show'? I use brads or glue dots when I can cover them up with embellishments.
The vellum glue dots? No, they don't show, but they also don't stick, in my experience
I've never had problems with Photo Mount clogging. It is a tad messy, any spray is, but just do it outside or in a large box (I use a large heavy plastic bag that our comforter came in) and you're fine.
I also like to use washi tape, just a strip or two like scotch tape.
When I use a 12 x 12 transparency overlay I do not use any adhesive with it. I just place it over the page and put it in the protector like that and it holds fine within the confines of the protector and stays perfect.
I've used several of them and just placed them on top and put them in the protectors.