There's nothing wrong with that regulator - Assuming it's in good working order.
I agree replacing the low pressure gauge with something that you can more accurately set in the 10-20 PSI range is a good idea.
I have a couple of those splitters on some regulators. They work great. The flare fitting is the same as corny QD's (Obviously, that's what they hooked up to for soda)
They may or may not have check valves. I have a few that do and some that don't - Either way, all you have to do is cap the ones you don't use. Either with a flare cap and washer (Should have them at your LHBS) or just remove the ones you don't want and use a pipe plug and some teflon tape.
Hmm - Dual reg, manifold, = $$$. This is $4!
Damn right I'd use it
Don't forget the seal between the gauge and the Co2 tank - VERY important!
On the end of the tank fitting there should be a groove with an o-ring in it.
If the o-ring isn't there, just go to the hardware store and buy a hard nylon washer that just fits inside of the nut on the regulator. It'll seal right up.