I'm a well read grad student who's bluntly honest about all things, although I try to be most honest about myself.
Issue six is an epilogue: it takes place after, it takes place in Gotham rather than the in the Turtles' universe, and it takes place a good deal while after from what I can tell. Still, this issue, five, ends up wrapping up the portal storyline with a twist.
It's fun, it used a character I didn't expect to be the brains behind this operation, and I liked it enough to reread in the future even if it's not a complete favorite mini-series, or crossover.