I'm still not sure exactly what the issues are here, but will try to respond to what I think you're asking.
1. The test to see how much a little target warms up is just a way to compare the powers of the different lasers. If the manufacturers have correctly labeled their output powers, it will not provide new information. If you wish to do this as a check, it might work to take a small test tube filled with a mixture of all sorts of food dyes, to make sure it does a good job of absorbing all wavelengths. You then need a very small thermometer. Perhaps a little diode thermometer measured with a little digital voltmeter would work at low cost.
2. All the lasers will send light an infinite distance, if nothing gets in the way. Some have beams which spread out more (have more divergence) and you can measure that by measuring the spot size as the target is set farther away. You can also try using lenses to reduce the spot size. You'll find that some lasers can be focused better on distant spots than others.
3. "Visibility" depends on who is viewing. If you were to build an automated system, you'd still have to calibrate it by comparing to how visible you thought the beam was. You could try to see how far away you could put a white sheet of paper and still see the laser spot. The answer will depend on things like how much other light is around, whether you have any color-blindness, etc.
(published on 04/11/11)