Exactly what we needed
We bought this plugin back in October 2011 to help us manage shipping for our website.
At the time, we had a need for one flat-rate shipping option for our 'home' country, and a different flat rate for 'overseas'. After a couple emails back and forth to work out the details, we purchased the extension with installation and the developer installed it twice for us so that it would do exactly as we needed (one installation acted as the 'home' rate and one the 'overseas' rate).
Fast forward to a week ago. After a couple of years of successful sales, made easier through the use of this extension, we decided that we were going to try make shipping easier for our customers again, this time by charging only once, total, for highest shipping rate only (if they have 2 items, one's shipping is $10, and the other $5, it would only charge $10, not add them both for $15). A quick look at the settings for the plugin we had installed showed that it wasn't able to do this.
A quick google search for what we needed had me come across the Amasty page for this plugin again - and the updated version did exactly what we wanted, again!
After some more back and forth with the support folks at Amasty, they updated the unique installation we had on our shop so we could continue to use the plugin, but with the now added functionality they had included since our initial purchase and installation.
In short, this plugin does exactly as described. I've had a great experience with everyone I've contacted at Amasty, and highly recommend them.