You should definitely use 2.55MP. While not unusable, 2.53MP introduced bugs which broke some things, particularly assembly programs.
Brandon Wilson wrote about this on his website saying:
As you might've read about by now, TI released their impressive yet horribly-unstable OS 2.53MP (MathPrint) for the TI-84 Plus and Silver Edition. Since its release, there have been reports from all over the internet about assembly program (and BASIC helper program) instability and incompatibilities.
I tracked down the bug that was preventing xLIB from working correctly on OS 2.53MP: there's a bug in TI's parser code which they introduced when trying to refactor all the code that sets 0,(iy+7). After calling the parser hook with A=1, if the parsing operation is canceled by the hook, then the OS incorrectly sets 0,(iy+7) when it should be setting 0,(iy+6). This causes problems all over the place.
To patch this issue, you can (in the 8XU OS upgrade):
Change 6B5Bh to: 06
Change 6C85h to: CD D0 7F
Change 5C00h to: CD D6 7F
Change 5CA7h to: CD D6 7F
Change 607Dh to: CD D6 7F
Change 695Ah to: CD D6 7F
Change 6BFBh to: CD D6 7F
Change 7FD0h to: 21 01 00 22 61 96 FD CB 07 C6 C9
It's kind of sad that I have to fix this bug for them, but a patched 8XU OS upgrade is available here.
I hope you take notice of this, TI, so that you can fix this and help everyone out, students, teachers, and "enthusiasts" alike. I'll make a deal with you...I'll take down your patched copyrighted 8XU if you fix your own bugs.
He created a patched version of 2.53MP to fix this, but 2.55MP has these fixes as well as the stat wizards you mentioned.