The Go cutter only takes Go dies. I have the GO because I do like the dies and was able to get a good deal at the Road to CA show a few years ago. Also, you cannot use coupons at Joann's for the dies - but I buy mine when they go on sale at the Accuquilt Website and want enough to get the free shipping.
It is true that the block sizes are set - but when it comes to cutting out the Double Wedding Ring and the Apple Core quilts, anything with curves it is fantastic and way easier than using templates. I have several circles, triangles and tumblers. I like that all the pieces come out the same size. For best results using the cutters it is best to starch the fabric before cutting.