A watt meter is a MUST HAVE. With the motors now having variances in KV values from what is listed in the specs, you can hurt something very easily by guessing.

I love my Astro meter. Mine is ancient by electronics age. I even hacked it with an rx pack so it's even more accurate, like the newer versions. Using the pack to run it, instead of drawing of the plane's pack it's way more accurate on the little stuff. Simple on off switch lets me run it with the rx pack or with out it.