Mag wheels, as mentioned, became a generic term for any wheel that wasn't just steel painted factory rims and used hub caps or wheel covers. Factory wheels that weren't painted but polished or chrome plated were also referred to as a mag wheel. If I recall correctly, one of the main reasons for not using magnesium wasn't just price. They were very dangerous when a vehicle caught fire. Evidently, once magnesium gets hot enough to burn, it is very difficult to extinguish as it makes its own oxygen. I recall way back when while we were camping out on an island in the middle of a lake, one guy brought some granular magnesium powder. Well, he put it in a pot & set it on fire. Well, it scared the living sh_t out of us as it burned right through the pot and the metal stand under it and kept burning through the ground until it hit water and still continued to burn. It burned in the water until all the powder was used up.
Those slotted mags have always been my favorite style. They are easy to clean & easy to check your brake drums & /or discs / calipers for heat from dragging. They were the first ones I ever owned. I bought them for my first car, a 65 Dart coupe. The ones I bought were made by Fenton, but I think I have used almost every brand made. I know that I had Ansen's, Et's, (AP's "Appliance"), & American Racing for sure. I found out recently that American just stopped making them. However, Thank God they are still made by Indy and in a large variety of sizes, even 17". If I had money to burn, I'd have put them on every vehicle I ever owned. Front wheel drive pretty much played a big part, due to the offsets, in my opinion, which did them in. I believe that Mag wheels in general, not only enhance a vehicle, but, since you can see brake components through the open areas, it encourages keeping your brake hardware and any visible suspension components clean & painted, which is a good thing! It also makes a vehicle more unique than a stock setup. Thinking back to my old Dart. I jacked the *** up to clear big *** tires, which scared people away who thought my car was fast. The joke was on them, it was still a stock slant 6! One other thing; mag wheels also draw attention from law enforcement, which might make you more inclined to "behave yourself, lol!"