but that doesn't mean that you need a thermometer to maintain temper.
if you're practiced enough to get the feel of the chocolate while you do have the thermometer, you should be able to temper without it.
i never use a thermometer but always test the temper before i fill molds etc. don't usually have any problems. while temperature is important, it isn't the only factor that affects your temper: time and agitation are also important as long as you have the proper seed crystals developed in your chocolate.
I want to second that opinion.
One of the reasons I stopped using a thermometer when hand tempering is not because I'm showing off my skills (well, maybe a little
) but because here even in the temperate (no pun intended) weather of San Diego, as humidity and other random conditions vary (air pressure? butterfly flapping its wings nearby?) , how long the chocolate is usable and how well it otherwise behaves (e.g. issues with sugar bloom) also varies, plus its a good way to learn how far you can go... even though the window is indeed narrow, it's not as inflexible as you might worry about.
Also, sometimes I'll semi-randomly mix couvertures to vary intensity or just to average taste. (For example, I've learned some batches of El Rey don't taste exactly the same as the next batch... I still like Venezuelan chocolate the best, but their at-site cacao farmer quality control is probably random.) In that case, my mix may not be at the exact temperature specifications given... in fact, I may have no way of knowing.
Also, being able to work with the chocolate by hand also allows you more flexibility in how you temper, because really there are a million ways you can get there. For example, Michael Antonorsi of Chuao Chocolatier once suggested to me & my classmates that instead of seeding with discs, seed with a giant block of chocolate and stir until tempered. Then just fish the block out when you're ready, which avoids having to worry about unmelted chunks. If you can recognize the temper by feel, it's much easier to pull something like that off.
Just blindly raising to temperature X and lowering to temperature Y and agitating, and/or mixing N grams of melted chocolate at temperature Z is a recipe for self-torment in the long run. Besides, playing with melted chocolate should be FUN.