This review is for Comfort Quick Latch 6501QL. I use this mask with P100 filters to filter diesel fumes due to asthma. I only use this for anywhere from 5 mins to 1 hour at a time but I do find it comfortable. I love the quick release feature and would highly recommend that feature for everyone. I can wear the mask 'Released' until I see the need to tighten. After the diesel is gone, I can once again Quick Release until there's another need. I love being able to have this ease so I don't have to wear it continuously when there is a chance of irritants. Size: I'm not sure what to tell you. Based on other reviews and the size chart, I ordered 6502 QR (medium), it was too large and I couldn't get a good seal. The 6501QR (small) fits me perfectly. I'm 5'4" tall, 160# female. I hope that helps someone find their correct size.