We're not talking about a top fuel dragster, a 550 is like a ford mustang in this comparison. If you take 5 minutes and set up each die to the instructions, it is NOT rocket science to load a cartridge.So how many folks do you think can learn to drive by starting out with a top fuel dragster or a NASCAR cup car or maybe a GT-40 road racer.
It goes both ways.
In all seriousness, if you can read and follow basic instructions, setting up a 550 is about as involved as setting up an electric razor. I went from opening the box to loading quality 45 acp ammo in less than an hour. And that was having never loaded ammo before and with a few cups of coffee while setting up and studying the process/taking measurements, etc..
The danger in loading ammo is in the powder charge and OAL... whether SS or progressive, you are SUPPOSED TO CHECK those in either. So there is not safety difference as long as you do your part... the latter just saves you pulls.