I'll concede that use of the PTR can conceivably result in a problem, but in my opinion debris is not much of a concern. If a bit of sand or lime crystal gets caught in the seal, merely opening and closing the valve again will flush it out. Frequent use of the PTR can, however, result in deterioration of the PTR's rubber seal, resulting in seepage - the PTR is not designed for every day use like a faucet valve. On the other hand, occasional opening of the PTR will keep the rubber seal from sticking, a not uncommon problem with PTRs that have not opened for years. The occasional use we are talking about here, maybe a couple times a year, is not something I lose any sleep over. However, the alternate methods work too - with perhaps a bit of running back and forth to open/close faucets if you don't have an outside faucet handy. Like George recommends, I routinely open a hot water faucet after connecting to city water so that any air in the line bubbles through the heater tank, just to be sure the air head is maintained.
For some reason, when I flush and refill my heater the tank usually overfills, or at least ends up with a very small air head. I like to start out with a nice one, so opening the PTR "adjusts" it in a jiffy!
BTW, you won't get any air into the heater tank if a gravity fill is used. The air bubbles back out the fill port rather than being forced into the tank.