The Ultima MG42 is an Shoei MG42 with a gearbox in it instead of escort internals.
The Shoei MG42 is very reliable but you should use HP air instead on CO2. Got to keep it clean and well lubed and it won't fail you.
If you are more familar with AEG's get the aeg version. You are looking at spending another $100-$150 for a regulator, and air tanks if you don't already own one.
The real MG34/42 drum mags fit on both versions, I made one for a buddy in Wisconsin.
PM me if you get one and the mag can't keep up with the gun.
Picture of a Shoei MG42 I hauled up from the parking lot for the Germans in my Mk3 cart.
Remember there are still rumors about the china MG42/34 circulating.