Hi Rayna,
I had never heard of the Magnapool, but after a brief perusal of their website I can offer the following opinion: it may work, but you can get similar or better performance with less money and goofy pseudo-scientific language.
It sounds like it's a salt-water chlorine generator that uses potassium and magnesium chloride instead of sodium chloride. Without knowing more details than their website offers, it's not possible to know if their system produces enough chlorine to sufficiently sanitize the pool. The verbage about it being more ecologically responsible and balancing its own water is bunk.
Adding magnesium chloride to your pool water is a bad idea. It is much more likely to cause damage to decking and coping than ordinary salt is. Potassium chloride is fine; it's just much more expensive.
I would say stick with a normal SWG, which will be much cheaper and is a tried-and-true technology. Straight and to the point, without all the eco-beauty-homeopathic babble.