I purchased several of the t.racks VM-100 Voltage Meter a couple years ago, as I use them in my rack-cabinets.
This is convenient as I only need one power outlet for each a makes it a lot easier when we are setting the gear up.
Also the fact that there is a build in lamp, makes it easy to see what is going on in the sometimes dark areas of the stage.
I had a breakdown of one of the units, but due to the great service at Thomann they replaced it at no charge within a couple of weeks, so thumps up to Thomann for this.
Highly recommended.