i always have two for this reason and those stick on ones really dont do the trick your much better of having one that goes into the water.
andy... i translate those claims slightly different. i believe within one degree, etc. refers to what you can expect your temp swing to be, not one degree from what the dial says but one degree in general. the same can be said for any temp setting device be it for a whole house, reptile cage or aquarium heater. i mean when i set my house temp to 70* it's because i enjoy my house being between 65* and 68* and i have come to know that setting it at 70* will consistently give me those temps (within 2 degrees of course).
also within one degree means in either direction... so it's one up or one down... which means a total of 2 for a swing...
If that's the case, maybe the heaters should eliminate the temp scale and just tell you to do it the way the old heaters worked. Turn the dial 'til the pilot lamp came on, monitor your temp, turn the dial a little more, monitor your temp, turn your dial a little more, monitor your temp........ It worked back then!