Checking the home page, MuseScore appears to have been last upgraded 25th of September. I'm not exactly trying to be its proponent, as I currently am actively looking for its downsides to quickly figure out if I can live with it, but I haven't had any trouble with instruments, namely I currently have a contrabass, a viola, violas, drums and a harpsichord, all of which appear to have three different parts each in the mixer (for just the instrument, a tremolo and a pizzicato versions), and I frankly have no idea how you use them, but I suspect that having them is a plus.
I found a couple of negative moments also. First, I wasn't able to locate bend. Second, it appears that after adding new notes you have to reload the piece to hear them in a correct dynamic (thankfully, you don't have to restart the program, as there is a reload button). And I had to fiddle with changing tempo in the middle of a piece a little, namely, it appears that it can't edit the tempo marker after it's been set, and if you change your mind, you need to delete it and set anew. Addendum:Another problem with MuseScore, which isn't technical - by default the essential panel is hidden, which cost me some fussing in the beginning. And you can't remove notes so that the following ones take their place, if it makes sense.
I believe that exhausts my list. I guess, I might as well submit my observations to the developers, if I feel like it.