I have a pair that I used down on La Palma and here in the UK. They are very nice, at least the Vixen ones, and give interesting wide field views. I would say that they may not help too much from light polluted skies but form dark skies they are very interesting. I suspect the other ones (Kasai and other branded versions) are Chinese clones, hence the cost differential. They do have their uses but I suspect that they maybe a limited use piece of equipment.
Owen