The specialized voltmeters for R/C are the analog "ESV)" (Expanded Scale Voltmeters. There's a couple of digitals showing up labeled for R/C use... but that's another story.) Compared to a good quality digital voltmeter... the ESV doesn't have any advantage. The ESV is a big improvement on trying to get a reading on a RX pack with a standard analog multimeter. A good digital meter will outperform the ESV every time.

I prefer the glow "ignitor" which is a C or D cell NiCd and glow plug clip all in one unit... no wires to get caught in the prop. The Power Panel with the glw plug "driver" (a large resistor and a rheostat for fine tuning, with an amp meter indicator) WORKS... but the wires are a big hassle. The C cell size Glow Ignitor will give a lot of engine starts between charges. When I fly a LOT (5 to 10 flights per session, 2 sessions a week) I charge mine once a month. (and I'll be loaning it to others... so it averages over 100 engine starts per charge.)

The fingertip prop balancer by Great Planes is the cheapest I'd rely on.
You CAN balance a prop by putting it n a music wire, or brass tube and spinning it. Before the first spin, mark one blade with a magic marker, and note if one blade tends to be low every time the prop stops spinning. Lightly sand the FACE of the heavy blade. That will rough in the balance of any prop, and is adequate for general flying until you can get a good balancer.
To be accurate... you need the balancer rig that has a stand.

Prop balancing is important to consistant engine operation. an imballanced prop leads to fuel "foaming" in the tank, mixing air bubbles with the fuel going to the engine. This makes the engie very hard to adjust at best... and can cause lean engine runs (damages the engine) and can cause unexpected loss of power at a critical time. (steep climb from take-off, not enough altitude or airspeed... engine dies and the plane is doomed.)
Consistently using imballanced props can also lead to premature engine bearing failure.