I have at least five PPR units. The least is an Air Cap II. It provides light positive pressure and is very easy to wear. I use it for light filtration tasks.
I have a Trend Airshield, which I used to use a lot. It is very good for filtration, but a bit cumbersome.
I have a couple different helmet units with a PPR pump. One is a plug-in to a countertop unit, and the others are belt worn compressors.
I have a big Paint booth style unit that is so loud in the hood, I never use it.
I have a full-face mask unit ( think of a Fireman) that I use for hazardous chemicals and cyanide. It gets its air from one of the pumps for the hood units.
Each has its attributes. If I had only one, I would have the helmet unit with a face shield and light weight chin bib.