Two basic questions:
(1) What are the immediate practical applications?
(2) How qualified must the user be? (The "all you have to do is supply a probability model" part is worrying :-/)
Basically, if you have your own dataset that you wanted to compress with a special purpose model, you could try doing that. You could try out compression-based tricks for computer vision, like in this paper. You could use it as part of an information theory course if you wanted to show students a real example of compression in practice.
In my view it is quite easy to use, but you still need to be a programmer with some knowledge of stats and information theory.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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