I thought this was frowned upon as the glass can damage the print? This is what I wanted to do originally as its significantly cheaper to buy an off the shelf frame in 24 x 36 inches, but I've always read this was a bad idea as the print will stick to glass, so I chose to use a mat board.
It can be, but so much depends on your own personal valuation of the prints, market valuation of the prints and then the environment in which they'll be in.
For instance if your prints would be in a room where there is a window that will let in direct sunlight then you'd want UV glass. if its a theater room then i reckon sunlight is no issue. Is it in a basement? is it relatively damp area? or a room where it gets hot and humid? Lot of factors .... They do make some spacers that people have put in place to keep print off the glass in stock frames. On my favorite pieces I go "all-out" and that includes mats , frames etc and that cost a lot of money .... but then I have other pieces that while I enjoy them I go cheap on the frame and sometimes use either a wal-mart frame or one from hobby lobby or Michaels etc. that is stock. However, you won't find an old valuable stout in one of those frames unless its there for a specific reason. (temporary staging area to flatten a print real good before properly framing etc)
So the personal valuation and market valuation comment is in reference to what the poster is worth to you? If there is no attachment to the poster (say, attending a screening or concert for the poster) and a person only ever attaches the value of which they pay never intending to sell or concerned with it then do what you feel is right for the enjoyment of your $50-75 poster.
But if there is ever the small chance of possibility of moving those posters on one day then invest in a mat or spacers to keep the print from being one day plastered to the glass.
I personally would never put a black mat in a black frame as it just sounds ugly to me. if you want a uniform look then I suggest perhaps just spacer and stock black frames. Uniform look will def help the overall theater look classy and have that stock photo appeal it sounds. However colored mats that compliment each print sure do add that bit of personal flare that gives the theater more appeal and character as to whom the theater belongs to.
I've seen where they've added another color for me by cutting the mat and it was black ... meaning the mat was (in this case) red but the back was black. So maybe even a "future proof" like suggestion is that you get mats the colors that compliment the prints but the backs are all black. Then you can decide which way to go and if ever want to change seems it'd be an overall cheap fix since you wouldnt be purchasing the mats again they just flip them around. But ... I'm no framer , and maybe that wouldnt look right on how the bevel is cut, or perhaps (like I think they do most) they put acid free removable tape on back of mat print?
@Jason Bourne might be able to offer some insight on that part as he operates a frame store locally.
Personally I play the life of chance perhaps far too much as I have prints stored in EVERY which way and have had many like that for years and still no damage. Got prints in flat file (now) got some in portfolio, some in wal-mart cheap frames, some in hobby lobby stock frames, had some in tubes for a year + , had prints on prints on prints stacked up with nothing in between, (no bleed through) and all of which in a basement. Just got done moving them all into a flat file that wasnt framed and all was fine. Have exchanged prints out of the cheap frames with years going by and no issues either. I think the scares have more to do with the environments in which they are in temperature and moisture wise....