The magnifier allows you to quickly and effortlessly organize your slides without going to the trouble of having to use a projector. Unflattering slides are consequently not presented during important lectures or presentations, leaving you looking professional instead of embarrassed!
This is just about good enough for the purpose I bought it for - to view a set of 35mm slides on a makeshift light table for a one-off project (which is to digitise a small proportion of my collection). It is probably more cost-effective than buying a projector for that kind of use. However, the lens distorts outside the centre which means you have to move it slightly to see detail at the edges of a slide. Think it's a bit over-priced for what it is.