Wonderful Rated 4 out of 5 stars
I've been using this for ages, and I find it slick & stable. It sometimes goes a bit dodgy after an FF update, but the fixes are out there and effective.
Only niggle: if there are more than 20 new items in a feed - which can happen quite legitimately - it won't pick them all up.
Now 5* Rated 5 out of 5 stars
Now that I've found (or you've added) the "Don't mark changed items as unread" option under feed properties, this is a 5* top class act.
Brilliant! Simple + effective: who could ask for more?