I really liked everything about them when I first learned. It's a clever solution, lightweight, usually easy to operate... But I could not get them to work as advertised without a lot of adjusting sometimes. And I also still tied safety knots with them. I ended up going back to straps because I have to hang short distances quite a bit and it's just a lot less hassle with straps.
I don't think whoopies have as much novelty unless you hanged with other systems with more knots and hardware first. Once you do that you can appreciate their minimalistic brilliance.