I have a Garmin 196 and find it excellent apart from one annoying fault. It seems the natural frequency of vibration of the mighty C85 on the Luscombe concides with that of the batteries and they vibrate. A momentary loss of connection is the result which makes the thing power down. Others have had the same problem. The remedy I use is some strips of foam draught excluder stuck on the inside of the battery cover to help stop them vibrating.
The onboard database has a lot of information in it, some of it, like frequencies and airspace, is subject to change, other parts like the location of airfields and towns is not.
Needless to say I don't use it to the exclusion of the chart so I rely on keeping the chart up to date and watching NOTAM. It's backed up by NavBox Pro, for which I do subscribe to the update service so my frequency lists and airspace are up to date when I am planning.
The 196 comes with one free update and I haven't felt the need to update since. I have however updated the system software a couple of times from the Garmin website. Watch out though because the update process is likely to wipe out all of your personal waypoints and stored routes.
CAA Chart Updates available
here.
Mike