Mostly "legalese" to keep the dumb people from eliminating themselves from the gene pool. When I had a TT, I used one and never had any issues with using it on a spot that I wanted to camp on. Never had the desire to park on hill's slope of more than 3%. Like anything else, you chock first, then put the jack down. I got rid of my manually adjusting foot and used the Fastway foot for a fairly long time (about 3 years) and never had any issues with it. Start the jack down and the first couple of inches of travel suddenly becomes 8" of travel. Used it on my Lego blocks and never had an issue, but, I always firmly chocked first and I used the X chocks. If the trailer can't move, neither can the foot. Installed properly, the foot locks to the jack post pretty well and the trailer would have to roll away (not merely jiggle) from its position to get the foot to collapse. If it did collapse, besides the shock of the 6" drop, it wouldn't hurt anything (as long as the TT isn't free wheeling on its own) as the foot is designed to be used on its side for those instances where you don't need the 6" drop. I think in the years that I used it, I used that way maybe twice.
If I got rid of my 5er and got another TT there would be four things I'd change out before my first trip: Jack antenna, power jack (if the new one didn't have one), the Fastway Flip Foot and the Fastway self-coiling breakaway cable. Actually, I'd negotiate those "enhancements" with the purchase contract.
My 2 cents, your mileage may vary...
Don
Bronwyn
Down to 1 kitty...J-Lo, the princess
2014 Thor Tuscany 40RX
2015 Jeep Cherokee TrailHawk Towed