This along with a 40mm cartridge adapter and a CBRN filter cannister makes a damn fine full face respirator. In a former life I worked as a field tech on hazmat cleanup sites where PPE up to level A was required in some areas. Having worn various respirators every day for weeks I'll tell you without any reservations that Scott masks are the absolute best in terms of wearability, durability, and maintainability. On top of that they are totally modular and can be easily converted from a plain old respirator to a powered resiprator, a supplied air respirator (air hose from a tank/compressor), or a SCBA setup. There's a real good reason that Scott pretty dominates the market for Fire Department issued SCBAs. They work and you can stand to wear it for long periods of time without issues. Issues like the small narrow straps on the other masks that will stretch out and cause you to loose seal, dig into your head like barbed wire and cut you or just hurt like hell after 4 hours or so, etc....
You need to do a little leg work before you run out and buy one.
1. See if you can find a safety supply company that will size you and let you try on a few masks. If you don't get the right size mask it will not seal properly and/or be real damn uncomfortable. Fischer Scientific (sp?) will do this for small companies but I'm not sure about individual customers. You ain't gotta buy it from them but you DO need to be properly fitted. Realize that wearing a respirator sucks. Some suck a lot less than others.
2. Get a sturdy bag to carry the thing in and some extra canisters. Keep the respirator with a filter mounted sealed in an airtight plastic bag inside the carrier til you need it. Otherwise the filter will absorb crap from the ambient air and may not be any good when you need it. The rule I was taught was replace the filter every thirty days if it's stored in the open air or every year in a sealed ziplock bag. If used in an operational environment replace it every 24 hours or sooner depending on what kinda crap you are in.
3. Practice putting the thing on every once and a while. With it on go out to your truck and try doing stuff. I'd be very careful about driving with it on because if someone sees you with it on they're liable to have a brain hemorrhage and call the cops thinking you're a friggin terrorist.
4. Realize that there's a lot of stuff out there that is bad not just to breathe but just to come in contact with period. Consider getting a complete suit with a hood, boots,and gloves. You can get a regular old impermeable hazmat suit or a milsurp charcoal suit. The hazmat suit is better in some ways like useable life, ease of decontaimation. It's a real bitch to wear though. You'll be amazed at how much you sweat even when it's cold because it's gonna stay in the suit with you. The milsurp charcoal suits suck 98% as bad and will have to be thrown away after operational use. You can't decon them.
5. How are you going to get out of a contaminated suit? If you are by yourself you need to have some industrial bleach & water and some way to hose & scrub yourself down very very well from head to toe. Decon is not fun. Self decon is a real bitch and will take a lot of time.