Sergio,
I have used the Trend Air Shield, Trend Air Shield Pro, the Triton PRA01 Powered Respirator as well as the 3M AS400. All of them work well, however I prefer the 3M AS400 and use it. It is by far the most comfortable and most unobtrusive when in use. After all the best protection is "the one you use". With all the others I was always finding reasons not to wear it and then regretting my decision when trying to breathe the next morning.
Enjoy the fresh air!
Doug S