This is a gizmo I invented a while back, in Irish music players keep their palm on the tailpiece or on the section of strings behind the bridge, I really don't like doing that, tension builds up in my arms/hands/whatever, the natural place for me to have the pick at is more "upstream," I guess the term would be - towards the neck. I've noticed this is only a problem with me when it comes to full size instruments - the other day I had the honor of playing a very nice late 30s Gibson Granada and I could get my palm down on the tailpiece OK if so desired. My banjo dealer tells me the Granada had a slightly shorter scale length than the Silver Bell and Challenger I usually play, so maybe I'd be more at home with a bit smaller banjo.
At one point it occurred to me to jack up the arm rest which works a bit of course but my palm rest works even better. The Silver Bell banjo pictured here didn't come with an arm rest anyway. I have an old Gibson TB-1 with a pick guard and I messed around with putting that on the player's side as well, that sort of worked. I've also made a bunch of variations on the model you see here, including a shorter one, a sloped one, one that's shaped like a 1/4 section of a circle - the "pizza slice" model? But a simple bar gets the job done as good as anything.
I play Irish music with everything "fingers up" and perhaps this will also be of interest to jazz players, no more need to drop the fingers down for single string stuff. These are very easy to build - just cut out some 1/2" (=25 mm) plywood, sand out the bottom with a belt sander so nothing touches the head, drill holes for leather cord. I've bought a whole big bag of leather cords from a farm supply store too, no doubt you can get that online somewhere - the bag was only about $10 USD.
I've learned to knock a tune out of a whole mess of instruments over the years too and some of them I just don't get along with - I really dislike holding violins for instance, the whole rotating the arms/wrists business is actively unpleasant for me to do. My father couldn't rotate his arms at all so perhaps this is a genetic liability. But I have no trouble at all playing flutes both wood and metal, and the flute is famously "the most unergonomic of instruments," so your mileage may vary as they say. Perhaps my palm mute will help someone with their banjo playing, or at the least be of interest.
Was messing around with various types of mutes today and it occurred to me that you could stick something underneath the palm rest to cut the sound a bit - settled on a bit of thick leather, but all kinds of possibilities suggest themselves, and it's a lot more easy to adjust/remove than the proverbial towel-in-the-resonator, and less obtrusive than clothespins on the bridge. Indeed you could have a rest on the floor side of the strings with mute material in place expressly to control volume.
I came up with a simpler model - ripped 1/2" plywood in half with my bandsaw, belt sander to smooth out surfaces, and the cords themselves help lift the rest off the head's surface. This is better as the rest shouldn't be higher than the bridge itself, and requires much less sanding than making a model with feet.