Propeller versus fin drives
Two designs dominate. Fin drives (Hobie's MirageDrive on the Passport and Outback) move a pair of fins under the hull. Hobie's current versions have kick-up fins that fold back when they hit something, and the Outback's drive adds reverse. Fins run shallow and shrug off contact; the trade is a drive that is less intuitive to reverse with and needs the full pedal stroke to work well.
Propeller drives (Old Town's PDL, Native's Propel, Jackson's Flex Drive) spin a propeller on a lower unit. All three here have instant forward and reverse by pedaling backwards, which is the feature that lets you back off a snag or hold on a spot in current. The trade is a lower unit that must come up in the shallows and that weed and line wrap around.
Forward and reverse
Reverse is the pedal-kayak feature you will use most after forward. Every propeller drive here has it by pedaling backwards; the Outback's fin drive has it; the Passport 12.0 R's MirageDrive GT does not, which is part of why it costs less. If you fish structure or current, count reverse as necessary, not nice.
Shallow water, weeds and obstructions
Every drive hangs below the hull. Propeller units need roughly a foot and a half of water and must be raised in less; Jackson describes the Bite FD's Flex Drive Mark IV as auto-retracting in shallow water, with a three-position dagger board, which is a useful compromise. Kick-up fins fold on contact but still stop propelling when they touch bottom. Weed wraps a propeller and fouls fins; fishing line does the same. In heavy grass, a paddle or a push pole moves the boat and the drive stays up.
That is why no pedal kayak in this set is listed by its maker for moving rivers, and why the finder will not pair one with that water: rock, shoals and a lower unit are a bad combination, and a drive that hits bottom in current can turn the boat.
Drive maintenance
Rinse after salt water, every time. Lubricate where the maker says to, check fins or propellers for damage, and inspect cables and cranks. Jackson says the Flex Drive Mark IV's upper unit runs in a sealed oil bath and needs a rinse after every outing; Old Town states a five-year warranty on the PDL drive. Budget a small amount every season for wear parts, and expect the drive, not the hull, to be what eventually needs money.