I believe, at least in the past, the Deere concave was mild steel and the Loewen was an alloy.  The Loewen would be "better,"   if it were heat treated, but it was not, so the mild steel was actually slightly more wear resistant.   This came from a combination of sources including Loewen (ours is alloy), Deere (ours is better material then aftermarket,) and Terry (they're both telling the truth, but here's the whole story.)  Terry sold Loewen parts, and we bought quite a few from him, but he recommended if buying a new concave, getting the Deere.  At that time we could buy them for about the same price.  This was several years ago, perhaps longer then I remember...I think it had to be the previous combine but it might have been the first one of the ones we have now.  

I could see it being possible that Deere could be outsourcing the parts concaves now since I don't think they are building wide cylinder machines in Moline anymore.