Probably better in the little greenhouse. By out in the open, do you mean there is no wall (even a low patio wall) or structure available that you can put plants up next to in order to give them a few hours a day of shade? Maybe spend a day or two doing close observation of the shadows in the immediate vicinity, and you will arrive at a slightly protected spot. I keep most of my plants on our rooftop patio, but I still take advantage of the way the low walls create shadows for plants placed up next to them.
For small plants (<15cm pot size) I like to use 50% shade cloth. Bigger plants (15cm or larger) I don't hesitate to give full sun. We are in a very mild climate, which helps make that possible. Your results may of course vary.
Regular window screen is about 25% shade, if that helps you come to some guesstimate of what that greenhouse thing is doing for you. Just be aware of extreme wind events and fix it well so it doesn't fly away if a storm comes through.
