Ruger, only. There's no reason to go too cheap, "nickel and dime", if you actually want to evaluate a gun. I just bought a $75, 8-rd. OEM mag for my first S&W 908-simply to see how reliable the gun can could be.
A partly-torn, round, silver "State of Kentucky" sticker was on my old Mini 14 when I bought it in 2008 in west TN. This might have been carried in a prison, or with an LEO dept. in Kentucky.
The magazine (in 2008) was Not common in Mini 14s, because Ruger had not yet decided to produce OEM ("Ruger") mags for rifles sold in civilian gun stores. Long story.
My magazine had a perfect operation (min. 500 rds.---all-Russian ammo! Silver Bear!) and that must have been due to the fact that the mag. came with the rifle, which had been originally issued in an official capacity.
Even for my used Mini 30 in 2008, the OEM Ruger magazines were not Yet available. My Promag misfed about once every twenty rounds or so: stovepipe jams.