Glass and Mirrors - mirrors question

I'm planning on mounting two frameless mirrors in a bathroom we are refinishing and then framing them with a wood molding. My question is whether the quality of the frameless mirrors at Home Depot is the same as I would get at a mirror/glass shop. By quality, I mean do they retain their clarity, looks, etc. My second question is how to best mount these mirrors. I've read about using some type of adhesive, but do I then need to support them in some manner while the adhesive dries? Any other helpful hints from experience would be appreciated. Thanks in advance. Potential mirror sizes are~"36x"36 and ~24"x60"
I had posted this in the mirrors/glass forum, but I'm hoping the greater traffic here will give me some more input.

follow the advice from the original post and also request the glass company to seal the edges...........which will help prevent the reflective coating around the edges from becoming damaged by moisture......

Quality bathroom mirrors have special backing and edging to protect them from humidity, a major bath issue. Make sure you research and purchase quality mirrors for your bathroom application.