I have the Accuquilt Go! It's fairly small and portable. It's easier to store the cutter than the dies. The dies are all different sizes and need to be stored upright, not stacked on top of each other, because the weight can damage the cutting part of the die. I store mine in a closet.
Whether or not it is worth the investment probably depends on how many quilts you make and your health. It is definitely worth it if rotary cutting is hard on your body. Other than that, the advantages of the Go! are: (1) the cuts are more accurate, especially for triangles and odd shapes, and (2) you can cut most shapes faster with the Go! (The exception might be strips, since these can be rotary cut pretty fast with a Shape Cut ruler.)
I prefer the Go over rotary cutting because of the accuracy; no more worrying about keeping that ruler from slipping in the middle of a cut!
It still takes time to use the Go! I have to pre-cut the strips I am going to run through; however, these are rough cuts and not precise. I still have to iron fabrics before running them through. I can't run more than 4 layers through at a time. When the cutter first came, it was stiffer to turn and I could do only 2 layers at a time. Still like it bette than rotary cutting, though.