I currently own the jazz theory book by mark levine. It's very informative and I'm sure it's gonna take me a few years to get the best out of it, but I wonder is it still worth getting the jazz piano book or does it cover most of the same stuff? I'm personally not a very good pianist, but would love to get a better understanding of how to improvise on the piano itself. But I mainly wonder how much different this book is besides the jazz theory book.
If I'm not mistaken, both of the books have some stuff in common, but the theory is book is focusing solely on theory (duh), whereas the piano book focuses on the piano. The theory book has some stuff about the piano and vice versa, but both have stuff the other book doesn't. I would suggest that if you have the money (they cost around 30-40$ on Amazon), you should buy them both. If not, you could stick with the theory book.
If you want to improve on piano, you should buy it. It has many useful stuff about piano playing that the theory book doesn't.
This link has a brief summary of the book's scope.
Over 300 pages with complete chapters on Intervals and triads, The major modes and II-V-I, 3-note voicings, Sus. and phrygian Chords, Adding notes to 3-note voicings, Tritone substitution, Left-hand voicings, Altering notes in left-hand Stride and Bud Powell voicings, Block chords, Comping ...and much more!