I got the upgrade for our dolly for a dinghy with an outboard. The wheels handle the heavier outboard load nicely and float over the fine gravel and sand at our beach well. They do add width to the dolly which makes maneuvering a little more difficult but worth it for the beach performance. Our other dolly has the regular wheels on a small sailboat and it works fine on the same beach, but is a bit harder to pull up the beach at low rise when it's steeper and a longer run.
I purchased the 12' dolly with the large tires for a Mercury inflatable....it works great !!! Easy to assemble, and very easy to launch and retrieve the boat. Large tires very handy for use in sand.