A "homemade" voucher is a good idea. If you have the time, why not check out the websites of all the local flying schools (all those mentioned on here), print out details, and give them to your friend along with the voucher, so that he can make his own choice. Or contact Loop (
www.loop.com, or something similar; do a search) and get their list of flying schools.
However, if this is too much work or you don't fancy the idea, you're not taking much of a risk buying a voucher. But do warn your friend not to leave it till the last moment to redeem it. We got that happening all through last summer at the school where I instruct - people with Christmas present vouchers about to expire, and now we were booked up or the weather wasn't suitable. "But I didn't want to fly in the winter", they'd cry. Tell your friend that cold clear winter days are the best flying weather there is, and he'll get a far better welcome from any school at that time of the year. In the summer many flying schools are rushed off their feet and many instructors are exhausted. Not everywhere, before someone pulls me up on this, but quite frequently. It's to a large extent a seasonal business, so that's life.