I don' know whether I can help much because I've only used one design, which worked perfectly well because it was,in effect, an ordinary softbox that folds up like an umbrella.
But I know that some makes are really just an umbrella with a bit of diffusion material, these work like reflective umbrellas, which means that they can't be placed close to the subject so can't produce soft light - maybe other people have experience of that type?