Dunco borderless (glass) enlarging easels - opinions/ experiences?

Has anyone here used the 30x40cm/ 12x16" or 40x50cm/ 16x20" Dunco borderless enlarging easels that use a glass platen to hold the paper flat? How did you find them in terms of paper flatness, ease of use, potential newton rings etc?

Just to make it clear, I'm not wanting/ needing opinions about borderless vs bladed easels.

Hi Lachlan, i used these easels for decades to make contact prints from 35mm negatives up to 5x7" on glossy Ilford RC paper.
I never realized any Newton rings. Even the surface of glossy RC paper was rough enough to prevent Newton rings.
Not to mention fiber paper.