Hi Jamie -
We store all our press contacts in Tessitura and pretty much only use WordFly for sending out press releases/invites/etc. Before WordFly we used TMS. We haven't had any issues (other than people errors) and we love being able to tell if press are actually opening emails and can filter that out for follow up emails etc.
If there is an emergency press release (like a cancellation or whatever) our staff can still manually send out an email on the fly by pulling a list from Tessitura.
The one then I will say just from a time standpoint is don't over design the media releases. We scaled back on the design quite a bit when it was just taking too long to do a release turn around because we were waiting for various design pieces.
HTH,
Heather