Go with the GPS type
Unless your planning using it on land, don't see that 24 hrs or 48 hrs will make much difference unless you have a liferaft onboard
Have been told that any GPS equipped device of this kind will take 30 mins from a cold start to find where it is in the world.
You should factor in Average cold start times when thinking of purchasing.
It should float. It should have a strobe and some active way of telling you its transmitting.
A strong pouch that can be securely attached to yourself or your LJ.
My criteria for a repeat purchase.