I have the mira cm-7m, the one with the two small eye windows. I've used it irl in hazmat situations. You have full vision, the windows are right where they need to be. And in my experience I would not want a full face window as the likelihood of you hitting something and cracking the whole thing is much higher.

I've gotten it to seal just fine with a close cropped beard (1/2 inch) and the tear gas should be stopped by just about any filter. The full expensive cbrn filters only last for about 20 minutes until the reactor element inside that kills the organic compounds with low boiling fades, but in my experience will still work for longer against OC, tear gas, and your standard industrial fumes. Combined filters will get all the above with the exception of things like mercury vapor and such, for half the price. So if you're playing the odds, 2 filters that nullify 90% of stuff could be better than 1 that gets everything for 20 minutes.