No, you don't need to jailbreak to run inavx. But it is handy for other things to do so. The jailbreak is just out for the iphone 5 or other devices running ios6.1.
Jailbreaking gives the user or his apps direct access and control over the entire file system. So you can install apps and tweaks that apple doesn't want you to have. Related to inavx, you can back up your charts and restore them from your backup instead of having to re download all of them, as an example. But remember that this power can be used for good, or for bad. You can make a mess of your phone
requiring a complete restore. You also void the warranty. Rooting a Droid is similar except it is easier and there is some support for rooting, even root enabled apps on the official Droid app repository.
The Samsung GPS
seems to be more sensitive than the iphone's GPS. But the Droid navigation
apps are not as sophisticated at this point in time. I am hoping we will someday see a port of OpenCPN
for droid. I guess to make it short, the jury is still out but either one would work okay for you. But Puh-LEEZE don't let this be your only method of Navigation! I think it is a good backup for another system, if you have a solar charger
for the device.
Understand that the best use of a droid or iphone for navigation is to turn it on, get a fix and see yourself on the chart, make appropriate steering
or sail corrections, and turn it back off.