This solved my problem completely!
I'm a younger adult, who other than changing a toilet flapper every few years, had no idea how to repair a toilet. Well, my older(probably from the 70's when the house was built) toilet started running into the issue of filling up extremely slow. I did online research and found out that one of the solutions could be replacing the entire fill valve.Well, Fluidmaster's name kept coming up and I found it at my local hardware store. I decided to just do a complete repair job, so I purchased this kit(flapper included), as well as a new vinyl water line, as my original one looked past it's prime.Needless to say, after some fumbling with adjusting the shank on the new valve, everything was replaced, and not only does the toilet bowl fill up super fast again, but the flush is more powerful.I enjoy learning DIY stuff, as I'm a young adult who will eventually move on his own, so this was a helpful learning experience.