The Sidekick was my first Leatherman. I loved it, but it has its drawbacks.
For one thing, the Sidekick's handles angle more widely apart from each other (compared to most Leatherman multitools, probably including your Super Tool) when the pliers are deployed. That makes using the Sidekick's pliers less comfortable than, say, using a Leatherman Wave's pliers. The handles are also contoured in such a way that my hand always feels like it's about to slip up (or down) towards the pliers.
I don't have a Rebar, but I have a Bond, which has handles that are similar to the Rebar's handles but thinner. They are less rounded than the Sidekick's handles, but the Bond (and Rebar) doesn't have spring-loaded pliers to press the handles outward against your grip like the Sidekick does.
I think for me, the wider stance of the Sidekick's plier handles make it less comfortable when I'm gripping something in the plier jaws compared to the Bond (and Rebar), just because the handles are farther apart and my fingers have to stretch out more to grip the handles. I think this is more uncomfortable than the Bond's less-rounded edges, because I don't have to grip the Bond as hard as I do the Sidekick (just to overcome the spring).
The Rebar will definitely give you a better tool selection than the Sidekick: full size serrated blade and file, better Phillips and flathead screwdrivers, and an awl. In my opinion, the only trade-off is the lack of outside-opening blades. But in many parts of the world, that's actually an advantage due to local knife laws.
I hope all of this helps you with your decision!