I hired an instructor to train some of my work crews in Lead Safe renovation work, because we are restoring a whaling captain's home built in 1800. The instructor relayed to us that beards are effectively a non-starter for traditional respirators. He also noted that the sizing of the respirator is critical too. Most people grab whatever happens to be available at the local supply house and never get fitted, despite the huge variation in face and head sizes. As a for instance, OSHA wants all employees who need respirators to be fitted by appropriately trained personnel.
I have a full beard and looked into the forced air respirators, but at an entry price of $1,200-1,500, I decided against it since I mostly push paper and would only occasionally use it for my personal projects. That said, I'm going to be glassing four wanigans pretty soon and would be glad to have one.