These cleats have been with me for over a year. They got worn smooth from walking on them. The previous pair I left in for two years and I had to drill one of them out. Advice for cleats: use some white lith grease on the bolts when you apply them. Use a long handled hex wrench or ratchet to tighten them. When removing them, drip on some light oil like TriFlow to work into the seams. Wait at least ten minutes for the oil to work in. Take something g sharp like n awl or a pocket knife or the tip of a new drywall screw to dig out all the crap in the bolt head. Even after that prep, you might not be able to fit your hex bit in. Next try a Torx bit of the same size. The wear on the bolt head might have screwed up the insides of the bolt head, but if you can mallet a torx bit in there, it should grip long enough to use a ratchet to back it out. Otherwise you will want to go to the screw-reverser bit in your drill.
Lesson: use that white lith grease first when applying new bolts!