VU meters are a guess at best. Watts are frequency dependent and the real measurement includes the frequency and distortion levels, This requires expensive testing equipment. I have had amps with and without power meters and to tell you the truth, you don't need them. They are just cool to look at but they don't add one bit of useful information. When you clip your amp, you'll know it. If you have a high power unit, you'll break your loudspeakers first before the amp gives up. Plus it's not a good gauge to judge if you are near the limit, your ears or your loudspeaker fuses will catch it before your meters tell you anything.
What is the name of the tool?
Forgive my absence of knowledge, but what is the name of the tool that one uses to measure the wattage coming out of ones speakers. I called it a watt meter to my family and got something that measures the watts and current coming from the outlet to the powered device I was using instead, for Christmas.