Plenty of folks are using them regularly and the project is just getting started in building awareness. I am currently making one myself. I was also given some sample filament to try out, and plan to share my experience. If anyone wants to see what people are doing with these, definitely check out the discord...
I'm familiar with the other methods of PET recycling you've mentioned, and projects such as Precious Plastic's or Brothers Make, but as you mention, they are great methods, but much more expensive and less accessible to everyone.
During emergencies, such as the pandemic, access to PPE can become difficult. Providing an open source design for the respirator allows for decentralized manufacturing to take place, mitigating the bottlenecks of centralized production and increasing accessibility. The filtered air provided by the fan is for comfort; it is much more comfortable to receive the flow of air from this mask than using an N95, as your lungs have to do less work. Also, the pressurization means that a perfect fit isn't required, such as with an N95; for this reason, PAPRas can work more reliably for people with beards, for example.