I have a Kodiak screenhouse 10x14; springbar use to make one very similar. For me the screen house was primarily for bad weather such that in the event we had high winds or lots of rain we could use the screen house to cook in, eat, store stuff, and just hang out. I wanted something that could be zipped up like a tent in the chance of bad storms or cold weather (or both). I also wanted to be able to use it as a tent for guest that came a long, which it does well as there is a 1ft overlap of floor on the walls that works well with a tarp underneath. It has two large doors on opposite ends that can rollup or double as awnings, which is great for use on the beach if you want to use it more as a canopy. It's a good shape in that it will fit over most picnic tables. It's very versatile. We used it a ton on camping trip to beach in October when winds were sustained 20-25mph with 30+mph gust and it held up well. Without it the trip would of been terrible.
I didn't get a clam shell screen house because the screens don't have covers and there is only one door. I've never used one, but the occasional complaint about them collapsing in a strong wind was a serious concern for me. There are a few threads on the topic with most posters having positive reviews of the clam shell. I think it depends on intended use.