I got my RY15526VNM trimmer a few years back. It's a 40V Expand-It type with carbon fiber stem. It works well but the original trimmer head was a real pain to open and load. It was a bayonet mount type which required herculean hands to grasp and twist and the filament had the bad habit of breaking on the inside which forced me to open it often. I was almost glad when it broke.
I wasn't sure this one would fit but it did and not only that but it works really well. Much easier to open than the original, easier to load new line. Easier to feed and somehow the line doesn't break as often. I'm very satisfied so I totally recommend it.