When comparing ScanSat vs Kerbal Engineer Redux, the Slant community recommends Kerbal Engineer Redux for most people. In the question“What are the best Kerbal Space Program mods?” Kerbal Engineer Redux is ranked 1st while ScanSat is ranked 6th.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Create maps
You can create detailed maps of every planet.
Pro Helps with landing the spacecraft
You can use ScanSat to determine the slope of the surface you're landing on and avoid hills and other obstacles.
Pro Much better than the stock scanning system.
The stock resource scanning feature finishes instantly, while ScanSat functions over a long period of time and the orbits you're in, like scanning satellites do IRL.
Pro Science boost
Provides a little extra science to help you in your career and science mode games- but you'll have to work for it!
Pro Helps with designing functional and efficient ships
Pro Shows important statistics when building crafts and in-flight
Shows important statistics when building crafts (mass, deltaV, thrust, ISP - while on Kerbin, in vacuum, or on other atmospheric bodies) and in-flight (all of the above + periapsis, apoapsis, orbital period, time to ap, time to pe and many many more).
Pro Provides customizable in-flight readouts of flight data
Pro This is not an autopilot
As opposed to MechJeb, which is considered "cheats". KER helps a ton by providing already available info in a very accessible manner.
Cons
Con Some users experience performance losses
This is only true when the window is open, it shouldn't affect the rest of the game.
Con Less readable than some alternatives
The same information is presented in a more intuitive and readable way by DMagic's "Basic Delta V" and "Basic Orbit".