Some lifts have spanner beams on the lower cradle to stiffen it. Other points of comparison are the drive-shaft bearing system, adjustability, maintenance requirements, product liability insurance and warranty. One is the low-profile HydroHoist lift, which will accommodate boats up to 30,000 pounds and eliminates the need for pilings. It rises and falls by forcing air into, and letting it out of, submerged tanks. It's suitable only for protected waters, as is Sunstream's underwater hydraulic lift.
Most manufacturers offer accessories for their lifts.
Keep children away from boat lifts and never permit them to operate one. Never work under a boat when it's on a boat lift. Make sure the power supply to the lift is adequate. Undersized wire results in low voltage, which decreases lifting strength. Make sure the dock is sound.