I bought one of those felt brushes years ago, they were using them for water troweling lime putty finishes where it isn't too bad to have a little extra moisture on the wall. It also kept the wall from getting too shiny so you don't piss off the painters. I never really liked using it for the same reasons as Nicm above, so there it sits almost brand new in my tool storage in my shop. About a month ago I had a job where they took out some walls in a condo, I was there to patch and match textures on the ceiling where the walls had been. There was a "handy man" and his "trainee" working there skimming joint compound on the walls. They didn't look like they knew what was going on at all. Kind of like "well I saw how they did this on Utube….", anyway the guy had one of those squeege knives and I thought what in the heck is he going to do with that thing? Anyway it seemed to work out okay for him, I couldn't see that it had any advantage over using a trowel or a set of regular taping knives. I'm pretty sure he couldn't have used a trowel anyway. Hey look there's an edit button!