dd is right. If you have any significant number of people, you are going to need at least two brands of respirator to fit everyone. The OSHA standard for fit testing tells you to let the workers select from varying sizes, makes, and models before you hook them up for the test. You also have to consider a mix of both silicone and latex-based rubber. Silicone doesn't last as long, but it fits some people who can't get a fit in rubber. Then, there are latex allergies to consider. It is a progressive allergy that gets worse over time and with exposure. Somebody can be fine one time, and a year later going into anaphylactic shock just from being in the same room with a baloon. No rubber for these folks.
You need at least:
two different brands
one or two models from each brand
two or three sizes of each model
both rubber and silicone for each size and model for at least one brand
You will still find somebody who can't get a fit.
Remember: Every respirator is disposable. You will eventually throw them all away. If you use a lot of them, it may be a lot cheaper to buy the more expensive ones and wash them. Re-usable/disposable respirators are not as reusable as you'd think. They get too dirty to use long before they wear out and can't be washed.