I prefer a sit on top kayak. It's a lot more versatile and a shore diver can extend his/her range quite a bit in addition to having a stable platform and storage space. Additionally if one is willing to buy used a sit on top kayak won't cost much more than your platform and it won't puncture.
If you prefer a sit top kayak, that's totally reasonable, but that's a very different thing.
This is 3x4 feet and weighs 14 pounds, so it's a bit easier to transport to and deploy at the dive site than a kayak.