Looks like a handy little gizmo when checking something out. I have something similar I made but mine has a Variac so I can alter the line voltage too.
It seems a shame to modify a pristine unit like that but I'd have to add a grounded line cord and outlet so I could use it on everything. Heck it doesn't even appear to have a polarized outlet so you will find a lot of 2 prong plugs won't plug into that socket anymore
One could just use a Kill A Watt to read voltage and current. These have the benefit of also measuring Power Factor and being able to display watts used over time (Kwh) so you know what it costs to run a device.
Still there is something great about having an analog meter movement to watch how current and voltage changes. And of course, vintage gear is always cool!