Well, you're definitely right about my love of tinkering.

Financially, I agree the cost of the heat gun is not justified for one use, though if you have or want one, then cost can be amortized over years of use. Full disclosure:
- Direct costs: glasses $2, mirror a few dollars, shrinkwrap 10 cents.
- Tools: heat gun $10

By cheap, I didn't want to pay for a commercial mirror just to see if I would like using one on glasses. So I slapped this together from items on the shelf. If it didn't work, then nothing lost. But the experiment worked so well that I still use it on my regular commute.

As for balance and heft issues, I'm sure an elite cyclist would balk. However, I do not notice the imbalance when I'm wearing a helmet.

You raise a good point about prescription glasses. I don't see the design adapting well. I'll add that caveat to the instructable.

Thanks,
Andy