A lock which restrains the control wheel is better than none at all, but to me, otherwise a last resort. Yes, it will lock the control wheel, but only locks the flight controls by requiring the internal flight control system to withstand the repeated pounding. I've known aircraft with bent aileron pushrods, cracked aileron internal structure, and bent and cracked pulley brackets from this. The Twin Otter crash in Moorea years back was attributed to gust locks being applied in the cockpit, and the control cables taking the ground gust loads.
The ailerons and rudder seem to generally be more vulnerable to gusts than a "down" elevator or stabilator.
I agree that on a PA-28, the stabilator is very hard to lock externally, so control wheel restrained full nose down may be the best you can do, but ailerons should have external locks on them - my planes ALWAYS do when they are outside.