It's a big difference, I went from an Ice35 to a FLX28, fish outside a lot in the sun. As far as I know, all the FLX have the same main screen & brightness. Seemed like I had keep to turning or tilt the humminbird when the sun was strong, no problem with the FLX.
Never tried the ultrapack but mine came with pro pack and I didn't like it. I'd think the ultra would be better as it looks taller, and the float storage/handle looks better. I think the neoprene cover is a must without a case.