Actually the more clever design is an actuator which contains more hydraulic fluid with the extended landing gear, like on the A330. In case of a hydraulic line blockage, it is easier to suck (cavitate) than to expell fluid into a closed tube (hydraulic lock). So gravity extension even works with a fully blocked hydraulic system.
You of course have the risk that somebody overfills the reservoir on ground, and it overflows when you retract the gear.