Split rims are on their way out. But thousands are still in use. The .5 designation is for new non split rims. 20/25 years ago "Bud" rims as used on most 40 footers were blowing on the highway. It was well known that they could blow when being inflated.
With that being said, I was in the business for a long time and never had a problem. Didn't have a cage but used a lot of caution and double checked everything, while the pressure was low.. 3 Piece Chevy's were the best and if done correctly were nearly impossible for them to blow. Ford's were poorly designed and difficult to tell if it was seated (Rim) correctly. Dodge was a little better than Ford but not much.
Even your modern passenger car tire can blow off, but that is quite rare.