I have a Garelick fixed bracket on my Whaler, with a 3HP mounted on it. Their instruction manual says "no trailering with motor attached", so I take it off when we go across the state on the interstate on vacation and put the motor in the trunk. However around town (4 miles to the ramp on city roads) I drive with the motor on, and tilted down.
My Stingray has an OMC bracket with gas cylinder and that 9.9 has never been off the bracket in 34 years. I don't remember what the owner's manual said and i don't have it any more. Nevertheless, they have never made a bracket even as good as the OMC. It is simply the cat's meow.
I guess its buyer beware. I routinely check the mounting bolts and the structure for stress cracks, so I don't worry. Also, I mounted a cleat on the deck just before the OMC bracket. I run a line between the cleat and the engine to add further security.
Now, having said that, if I ever had a Garelick adjustable bracket I would be afraid to have a motor on it even in the water! They wiggle too much for me.