The Fleet One runs off a dedicated circuit switch channel and will have unwavering voice quality every time you use it. That quality will come with a bit of latency, but generally will be very usable. You will be assigned an Inmarsat phone
number which can be very difficult to call from a regular cell or landline phone
(and quite expensive - generally in the range of $10-$15 a minute for the cellular user). Airtime for voice calls on the Fleet One will likely end up being more expensive than that for the V3.
The V3 uses VoIP technology so the quality should be good unless there's a lot of contention on the line. If that occurs (possible in a crowded marina or other areas with lots of satellite
users in one place) there is a risk of burstiness when the quality of the line is slowed down. (Think of what Skype gets like when your internet
slows down - warbling, drop-outs, and eventually could become unusable).
That being said, in most cases where contention on the line isn't an issue, the V3 will have pretty good voice quality, for cheaper prices than Inmarsat, and you will have the choice of being assigned a US-based phone number (makes it easy for family
and friends back home to call you).
So published specs on the Sailor Fleet One put it at a max of 120 W @ 10-32 V and runs on 12-24V DC. What you really want, though is the average. I would recommend checking out this article (Grant was a customer of ours) of a cruiser who had both an Iridium
Pilot and a Fleetbroadband 150 on board: Testing Sat phones | Cruising World
(Note: the Fleet One is essentially a pared-down version of the FBB 150, and power consumption
is about the same on both).
Published specs for the V3 put it at a max of 160 W @ 100-240 V AC. I'm not sure what the average is, although I would guess it's a bit higher than the Fleet One judging by the max draw.