Something else to keep in mind - tablets and phones aren't designed to handle the heat when in the sunlight. I use my iPhone for music on the boat, and if I put it on the dashboard on a sunny day, I get about 30 mins before it overheats and shuts down.
While I don't have experience using phones/tablets for navigation purposes on the boat, I have been playing with various Android devices for offroad/4x4 navigation since the first Android phone, the G1, back in 2008, and also have went through many Windows and Linux based mini computer systems with 8 to 10" monitors. Like anything else, they have their pros and cons. Screen readability outside of some the earlier devices was pretty poor, but like any modern cell phone, the screens now are pretty decent outside. I have no problem seeing the screen on the iPhone 6 outside, but it's nowhere even remotely close to the brightness and clarity of a screen on the chart plotters/GPS/fish finders/etc intended for a boat. I find the GPS antennas built into many of the less expensive devices are also poor compared to other dedicated devices. If you try to mount one inside a dash, you're likely going to be disappointed quick. The bigger name brands do seem to work pretty well though - Google phones, iPhones/iPads, HTC, Samsung, etc.
I've also found that mounting them can be a real bear. If your device of choice falls into what Ram mounts cover, you're golden. ProClip also makes a decent selection of bolt down mounts that work well, but also is a bit pricey.
What I'm now currently running is a radio head unit made by Joying that is a lot like an Android tablet permanently mounted into a double DIN radio chassis. It runs Android natively, has a capacitive touch screen, as well as a small radio amp built in as well as supports having an external GPS antenna connection. So I can push it down into the dash to block the sunlight from hitting the screen, and mount the GPS antenna on the roof for better signal. I'm likely going to end up putting this one in my boat, and buy a newer model for the truck.