Making only one mirror so far I found great satifaction in knowing that I made a precision optical surface with my own hands.
You have control over all aspects like your focal length and when to stop figuring as to how accurate you are happy with like a 1/4 wave or a 1/20 wave mirror.
I was happy to get around a 1/10 mirror.
You might save some money if you are planning on a big premium mirror but little mirrors I think its cheaper to buy one.
The grinding bit is a bit tedious but is great to do when its raining and the kids are in bed while you listen to the radio!
Will be doing a 8" next year the a 10" after that.
I should be getting the hang of it by then!!
cheers Gary