Opinions on GPS and mapping systems are like arseholes. Everyone has one, and they are all different!
I use a Garmin Legend HCX. Has a colour screen, and I have talkytoaster maps on a card. These are not as good as OS, but not far short; they are certainly good enough for my needs. I have Memory Map on my laptop and plot routes on that, then download to ther unit, and follow the direction arrow all day. Very seldom get the map out when on a ride, but carry it with me just in case. Works perfectly for my requirements.
Others will come along with their own particular setups, which all do the same thing but each in their own way.
Best thing you can do is
1) Wander into a decent outdoor shop that will have a range of units and see just how they work.
2) Go riding with someone who uses GPS and see how they function with it.
There is no "right" answer. What works best for you is the one you like best. Just like bikes really, everyone has their own preferences.