Hey, NYH -
I've been fishing with the ICE 45 for 6-7 years and love it. I didn't see the advantages of the 55 - 6 color display, and carrying case - being worth the extra $100. Per their own site - "Fits in a 5-gallon bucket: Every ice fisherman has a five gallon bucket. Use yours to transport and protect your ICE Flasher with ease.", which is how I transport mine. No case required. And 6 colors? Never seen one in action, so I can't really comment on the usefulness, but the 3 colors on the ICE 45 seem to do the job for me.
Good luck with whatever you decide.