The problem with avoiding an OO oriented approach is that they will quickly run into issues once their testing needs become significantly detailed.

Well - I tried very hard to make it easy to refactor from Test::More based test scripts to Test::Class based modules - so I'll be kinda sad if this turns out to be a problem to move to Test::Class once they hit the issues.

Better that they tackle good practices right off the bat and avoid reenforcing procedural programming that they are used too.

I certainly don't think Test::Class is a best practice. It's a way of testing, better suited to certain kinds of environment. I certainly don't use it for everything that I write. Adding complexity when it's not needed seems like a bad thing to me.