They look like a good product. I have a smaller version, open on one side and sort of square shaped. Only problem I found is the surface on most regular sewing machines is quite small and not totally smooth/flat. Even the free motion extension tables have uneven areas. I can do just as well wearing special gardening gloves to grip the quilt. It also helps go slow at least until you can do the motions smoothly.
Also, notice in the video the demonstrator is using a large, high long-arm machine mounted to a large flat table -- lots of area to move the quilt around. If you have the budget and space for a longarm (and frame) you have no need for the Martelli hoop.