We have one, probably the exact item you showed. It is in its third year of use on our front door, so it has had a lot of traffic from us and our six golden retrievers.
The sides connect to the wood door opening by some stick-on Velcro patches. Those lasted one summer then would not stick on any more even though I left them up all year. [I take down the screen and store it for winter.]
So, ours just hangs there but it still does a pretty good job of keeping out the flies.
The curtains hang from a metal bar, spring-loaded and adjustable to the width of the door opening, like some curtain rods are designed. Even set really, really tight, sometimes the dogs would explode out the door and pull it down [think: chipmunk alert]. So, I took a couple of 3/4" conduit clips [the metal kind] and screwed them in to hold the bar up. No more pulling down.
The magnets work fairly well. Not perfect, but decent.
All in all, worth the maybe $30 I spent on it, not sure but I think that was about the price.
I kept the box it came in to store it....