I've never used one. I may be the only guy who had a battery short out so I had to lift a 90HP OB by hand in a launch parking lot. I loosened the relief screw and lifted from the bottom of the lower unit. As I approached the fully-trimmed angle it got a lot easier to lift. The weight of the power head was balancing the weight of the lower unit. If your OB has trailering lock tabs that seem strong enough to actually hold something, use them. Trim/tilt the OB up until you can set the tabs. After setting them lower the power trim until it squeals. That will hold the OB down against the tabs, preventing any OB bouncing or tab movement. The OB will be balanced so the strain will be straight down on the transom.
One caution: I looked at a new OB a few weeks ago, and the little trailering tab on that OB didn't look very robust.
I use one. Looked at store bought ones, thought they were wimpy and overpriced. Easy project to just build your own.
Another thing I never thought of when I put it on. I think mine saved my motor when the trailer came unhitched (only time in 40+ years) and got up on the safety chains, the only thing that touched the pavement was the transom saver.