For what it's worth, it's the "_redirection_404" table that bloats. I don't fully understand how this plugin works, but it looks to be storing hits, possibly from everyone including crawlers, in this table. So I guess every time anything throws a 404, it logs the entry in a new row, resulting in a massive table.
Deleting the 404 logs in the Dashboard obviously clears this out, but if you have hundreds of log pages, deleting these is tedious.
It appears as if the "One Week" 404 log setting isn't being held to by default (as I've never adjusted these, but they have all been set to One Week).
With any luck this will make sense to the developer and a fix can be sorted.