I have HDS gen1 units on the console and the bow. I wanted units that I could link together so I could share info between the units. If I mark a waypoint on 1 unit I want to be able to see it at the other. I have no regrets adding the 2nd unit. The only advice I could give is get the biggest screens you can afford. To me it doesn't make sense to add anything except another HDS unit.

The big advantage of going with the HDS units in the 1st place was the fact that additional units could be linked together.