volt gauge or not?

On my 76 duster the amp gauge curcuit was incorporated in with the curcuit boarder on the back of the gauge cluster which at some time shorted and burnt a bit of the panel. I plan on bypassing it when I put it back together because I have lots of electrical add ons that would probably peg the gauge out if I kept it. As far as a volt gauge, I didn't want to install another big gauge that I would hardly ever use so I bought a volt meter that plugs into the cigarette lighter. That way if I want to monitor my voltage I can just plug it in.
This is what I bought, http://www.amazon.com/gp/product/B00962CQNC/?tag=joeychgo-20