To build a little on Sam's comments, the GRT Mini is a pretty simple installation. It's ADAHARS is internal. If you go for the basic Mini, all you have to do is hook up power, ground, pitot, static and the included GPS puck. Going to the Mini-X means adding a magnetometer; GRT has gone to a "smart" magnetometer that no longer needs to be installed in perfect alignment with the aircraft axes, so installation is again considerably easier than previous generations.
The internal battery on the Mini lasts a LONG time. If you back the brightness down from a setting of 10 to 8, which is still plenty bright, the battery goes well past 2 hours of endurance. I seem to like a brightness setting of 6 or thereabouts; I haven't tested endurance of the internal battery using this brightness setting, but I know I would be more worried about my personal endurance than battery endurance. Ours is the Mini-X with terrain and mapping. While we're not yet flying our project airplane, I really like this little EFIS.