I have the Parkit360 10K. The tires are plenty beefy enough to maneuver on grass, or pretty much any surface for that matter.
It's very sturdy and well made. My only issue is the tires on mine are beefy to the point that in a tight turn, they rub the folded up Robofoot on my power jack. I think the 5K tires are a little smaller and probably won't pose the same problem.
The way the Parkit360 works is after you lower the trailer onto the ball, you use a long steel rod (supplied with the dolly) and turn the base until it's tight against the coupler. Make sure to snug it up, otherwise there will be wobble forward and backward with the dolly since it balances on two tires.
At some point I'm going to grind off the yoke coupler and weld on a Bulldog Collar-Lok coupler, which will give me a few more inches between the coupler and the jack pole, so problem solved with the tires rubbing the jack.
"You can't buy happiness, but you can buy an RV. And that is pretty close."