I have a jotag sunfish dolly and a seatech laser dolly.
I've had the jotag for a couple of years now. Overall it's a solid dolly for the price. It's definitely a better fit if you have a older sunfish with the chrome edge. I have a newer rolled edge fish and find it's always slipping around because the front cradle is flat does not snugly fit under the the bow like my laser dolly. You MUST tie the bow down tightly before you pull it.
The other concern is saltwater. I use mine on the NC coast in the summer. The Jotag is a mix of steel and aluminum parts and mine has more corrosion than I'd expect from a marine grade product. The Seatech is 9 years old seems much more corrosion resistant.
On the positive side I like the jotag's solid wheels. Flat dolly tires are a pain but the Jotag wheels are not good at all on soft sand.
Final factor. Breakdown. The jotag does not break down nearly as easily as the dynamic and seatech. If you need to put in your trunk or a mid/small SUV the jotag is too big. The others come completely apart with no tools.
Bottom line, if you are around salt water, regularly launch on sand, or need to put it in a vehicle, spend the extra $$. Otherwise it's a good dolly for the price.