This is an awesome plugin! After using it for couple of months, I want to point out one issue and give one suggestion. Also have a question to ask.
Issue: I think the Redirection database is prone to corruption. One fine day I noticed that my home page was redirecting to my contact page (which is mydomain.com/contact/feedback)!!! I really do not know how this happened. I don't remember accessing/modifying Redirection settings/entries at all, but I noticed this issue a few days after I freshly created the feedback page.
Anyway, I resolved this by deleting the entire WordPress module and creating a new WordPress module and importing the entries back from a recent backup XML file.
Suggestion: Please add a verification step for the "delete" option on the Modules page in Tools > Redirection. Right now, if I mistakenly click on "delete", the module simply gets deleted without even asking me for confirmation. This is very dangerous and can cause a lot of frustration (as it did for me)! A confirmation dialog box would be extremely useful!
Problem: Coming to my problem, I had an old page mydomain.com/seminars/mp3player/index.html which was a HTML page. I have now redesigned my site and this page has been shifted to seminars/portable-mp3-player.
I have added redirects for seminars/mp3player/index.html and seminars/mp3player/, which are working fine. But seminars/mp3player does not redirect and gets a 404 error.
What regex can I add so that the same entry redirects seminars/mp3player with and without the trailing slash to the new page? I tried seminars/mp3player(.*) but it doesn't work.