Works great once you get one which fits.
The biggest problem with ordering a respirator online is that you can't fit test it. I first ordered a small based on 3Ms recommendation which is based on height. The small turned out to be too small so I ordered a medium. The medium fits just fine. It seems to me that measuring the distance from the bridge of your nose to your chin would be a much better basis for fit recommendation than height.
Now that I have a respirator which fits, I'm very happy with it. It's quite comfortable and fits well under my Hobart Impact Black welding helmet. The flip-down feature might be useful for talking to people but I find it more useful for enabling me to quickly dry the condensation out of the respirator. As long as I wear a welding cap underneath, I don't even notice the plastic head piece (I do notice it if I try to weld without the cap).
Overall, I have to say that this is the best respirator I've ever used.