I bought two different sizes of these rectangle frames off Amazon within the last two years. I really like them. They are not perfect and don't hold your project as tight as a wood stand likely would. They also can be a bit difficult to snap the holder bars on each side, but that is necessary. If they were any looser your canvas would slip out. I also read the reviews because I didn't want to buy something I can't use. I see that they also have the exact same product at Michael's for about twice the price (in my city). I am in the states, so I'm not sure if you have a Michael's by you.
I like the fact that the different sizes are interchangeable. I tried using both of the frames with each other's pieces and they work just fine. I have used the smallest and largest since the projects I tend to do will fit those bars.
I've tried snapping in just the top/bottom or the sides only depending on where I am on my canvas. This works well and doesn't warp the canvas you've already worked. All-in-all it was a good purchase. I don't know that I'm ready to spring for a more expensive wood frame since this is so portable and so much less expensive.