I have tanks throughout the house... would make for a hell of a heating bill. 
I was thinking about the alarm actually. Hmmm.... I could build some of those up I think.
The Aqueon Pro is actually the kind that I buy now. Most my tanks have them. I like that they are not glass. I also try to use multiple heaters i the larger tanks instead of the giant ones.
How do you notice wear on a heater?
I hear you - my setup is the same way, so central heating is not really practical.
You can buy the thermometer/alarm combos cheap as well at various places...I can't remember where but a friend of mine had one that was pretty cool - you set a range that is acceptable and then too high/too low it lets out an earsplitting beep.
I like that they are not glass also. Good plan on using more smaller heaters vs. larger ones (as to not cooking fish).
The only downside I've experienced with multiple heaters, besides the possibility of a slightly higher electricity usage, is that it's hard to get them calibrated exactly the same. So you have to fiddle with it, or else settle for one running more than the other. Not a huge deal, but it was frustrating to me.