On the Anycubic i3 Mega/Mega-S, Heated bed unit and the Ultra-glass unit are attached via sticky tape. But the alminium (heated bed) and the glass (Ultra-base) should not tightly attached, or it will be bended because the shrinkage rate of the Glass and Alminium are different.
From the above point of view, its better to use clip instead of sticky tape.
But too much height of clip also causes problem, so I just quickly designed a low height clip for Ultrabase, it is 5.5mm thickness.
Please print 4 of it, and attach to the side of the Ultraglass.
Added 5.4mm thickness version (v2)
Anything is OK PETG or ABS is recommended
If you use your heated bed temp over 60 degree, print with PETG or ABS is recommended.