Man, I felt this in my soul. Made the same switch about two years ago after wrecking my shoulder reaching over with the banjo all day, and the corner trowel just flat out gets into places the banjo can't reach. The trick nobody tells you is you gotta ease off the pressure on the second pass or you'll leave ridges the banjo never would, since there's no flex in that corner. Also keep a small sponge handy for the edges because that tool likes to drag mud past the joint line if you get greedy with your load. Give it a couple weeks and your wrist will thank you, plus your butt joints come out cleaner with way less feathering. I still keep the banjo around for big flats, but for tight butt work I'm never going back either.