There are many versions of the Diabelli available, but this comfortably holds its own with the best (among which I would include Paul Lewis, Nikolyeva, Anderzewski to pick a few.) Staier is a superb pianist, and sails effortlessly through what is a very difficult piece of music. Two things make this cd especially interesting.
The first is the inclusion of variations written by other composers who were asked to contribute. They are competent and interesting enough, but show the different league that Beethoven was in compared to most of his contemporaries. (The Liszt variation, apparently written when he was 12, is an amazingly virtuosic piece from one so young.)
The second is the instrument used - a fortepiano with plenty of range and volume, and with some interesting effects used occasionally. One sounds as if the whole instrument is about to collapse.
I won't rabbit on about what Staier does with each variation, but he's obviously put a lot of work and thought into the performance, and the whole thing hangs together and flows beautifully.
Get it - you'll probably love it as much as I do.