I recently attended a small jazz show by a group of old guys, all experienced and excellent musicians. One of the musicians played an arch top guitar using just a thumb pick for upstrokes, downstrokes, chords, backup, solos, the whole works. If I had not closely observed his technique, I would have assumed that he was using a flat pick — that is to say that his playing was not apparently different from what you would expect from normal flat picking.
During the break I asked him about his technique. He said that he had grown tired of dropping and losing his flat picks during performances. So he copied the technique of Chet Atkins, who he said used a thumb pick with three fingers. He said that it took him a while to gain proficiency in using the thumb pick, but after a while he was able to use the thumb pick to execute all of the strokes that we normally do with flat picks. And when necessary he could also use fingers.
I didn’t think to ask him about tremolo, which may not be a big deal on amplified guitar. But I did find it most impressive to observe well-executed thumbpicking. And I don’t know if this has an application to mandolin, but it might be worth $0.75 to find out.