It's incredibly hard to tell with aftermarket parts, all I can suggest is to compare the BMW one to the aftermarket one, you will quickly see if it is well made or not. My parts buying experience only keeps me away from most of the Chinese stuff which almost without fail 9/10 is junk.
There is almost no peace of mind with many aftermarket parts and mostly that is why they are cheaper, but look hard and you can certainly get some quality stuff.
Also the Italians are very good automotive engineers, and there are many BMW OEM suppliers in Italy, I'm running Italian manufactered waterpump, brake discs and pads and Korean suspension parts they are top quality, so why not.