I work for Flight Options and we have been using the Fujitsu model for some years now. I can tell you from experience that they are great. We were the first to get the Fujitsu and the first models were not as good as the newer ones. The early ones locked up a lot and were way to dim at day and bright at night. Fujitsu has worked with us and they have improved on these problems. The new ones hardly ever fail or lockup, the brightness and dimness has been improved. However during the day with sunglasses on and in direct light, you still can not read, must remove sunglasses. Updating is a breeze, about 5-15 minutes depending on the amount of updates. No more pulling charts, especially for us, when you have about 5-7 legs a day, big improvement.
Has far as having paper charts, my understanding is under a 91 ops, you do not need to have paper back up, under 135 you do need to have paper backup. Right now our Fujitsu's are not approved for 135 because we do not have them hard mounted, so we will have to start carrying printers and print charts for each and every flight. Not going to be fun, considering how much things change around here.
One other slight downside to the unit, with some charts it requires a lot of moving the chart around the screen to get all the information.
All in all, I enjoy having the units, and prefer them over carrying, updating, and pulling paper charts. They are very easy to use and have lots of capibilities. We have stored our ops specs and all company pertinent papers on there, eliminating carrying extra paper and freeing up space in the cockpit/plane.