Can't tell you about length of life or wether they are worth the bang for the buck. However for us trey are worth it. They are essentially zero maintenance and that's important to us as they are hard to get to in the Little class C we have. We installed two group 31 AGM batteries a little over two years ago. They also seem to take a charge faster from the 320 watt solar array we have. We turned the controller output down a bit for when in storage and we crank it up a bit when we are using it. Our converter goes into bulk mode at 14.4 volts and they seem to handle it fine. I'll defer to the experts on the board for how things should be done but we don't really treat them that special. The only other thing I noticed is that the voltage drop is very minimal under heavy inverter usage. Again I'll leave that to the experts on wether that is imaginary or real.
Hope this helps.