I bought a Universal carbine brand-new about thirty years ago, shot it for a while, then passed it along to my younger brother, who still shoots it occasionally. Neither of us has had a problem with it as far as reliability is concerned.
However, just as Dave says, not all Universal parts interchange with GI. On the one I bought, the trigger housing is a somewhat crude alloy casting held to the frame by a roll pin. A GI trigger housing can be substituted but won't fit the stock opening. Also on mine, a GI bayonet won't attach despite the bayo lug, not that this matters much.
So, I'd also rather pay extra to get a GI carbine.