There are two things ExtUtils::MakeMaker does that Module::Install doesn't do or tries to get "wrong." I wanted to have a WriteTests.PL file run just like EU::MM would do automatically. The "work around" is putting a system $^X, 'WriteTests.PL' into the Makefile.PL. Oh well. There's no equivalent to EU::MM's PL_FILES feature. I don't know that I really cared about that though.
WriteTests.PL generates a bunch of templated tests in t/ but M::I's generated Makefile won't use them because unlike EU::MM it doesn't just run everything it the t/ directory: it runs only those t/*.t files that exist prior to &WriteAll.
Oh well. This is easy to work around, just kind of annoying.