I have a wall in front of me when I squat. Works great. I used to have a mirror as my "judger" though Haha...Kentucky is great!!! I always hated seeing anyone looking at me when I lifted though.
A mirror is not a good judge of if you break paralell or not. Ever see a pic of a guy squatting that looks deep enough...but he still got 2 red lights? He got them from the two side judges because of depth. Unless one can see from hip heighth...it can not be acurate. There are zero mirrors in Louie's gym...and his guys hold some of the best squats in the world.
I used to think that I needed a mirror...but I guess I've got used to not having one. If I ever train in front of one...I cover it up with a large towel.
I do wish that I had a good squat or power rack though. I get tired of sitting up my drums for squat racks.
i dont use the mirror for parallel, i use it to keep my knees straight, and to check myself for form breaks. ie. flattening ankles, knees going in, hips shifting. for me squatting is much more than point a to point b.