Incredible module, takes excellent Moose OOP ideas and makes them fast, faster than anything, faster than raw Perl methods, faster even than accessors in other languages, combine it with Function::Parameters and you have Modern Perl with strict type checking and it's fast!
Note that this review is revision of my former review referring to the version 0.22 of Mouse because the former one doesn't in the least reflect the status quo, and that this caters for folks with prerequisite knowledge of what is called the family of Moose. Keep your nose out of my business if you dislike following those trends.
As you know, the module was written by Shawn M Moore at the outset, and then taken over to Fuji, Goro-san (aka gfx), and thus the present maintainer is gfx; consequently, all the users are lucky to be comfortable using the module.
In the meantime, the definitive differentiation compared with the earlier versions of the module is that by default the module is built as an xsub, and needless to say, the pure perl version only can be installed as well, as per your request. That leads up to as fast execution of the module as possible, including its start-up time. Insofar as you don't deal with meta-objects, Mouse can be a drop-in replacement of Moose.
Last but not least, recognize that Moose, Mouse, and Moo are never in conflict with each other. They have their merits and demerits each. You want to read the following article written up by Stevan Little:
"The Moose Ecosystem"