I have Radar on my current boat. It's an older unit (2005) but works.
I've only found it useful maybe twice on the lake. Perhaps the newer units are much more useful?
Keep in mind that most small boats on the lake are fiberglass, and often pop in and out on the Radar. Radar needs something to reflect its signal back to be seen, and fiberglass is transparent to radar. Perhaps a lot of this popping in and out is because of my older (2005) technology? I'm not sure if one of the newer technology devices would be better in this regard, or pick up smaller Radar reflections from the engines, or metal fuel tanks, etc.
Where it helps the most is at night, such as leaving the crowded Meredith bay, or Wolfeboro bay just after the fireworks ended, but having a boat full of eyes with their heads on a swivel is usually better.
We don't often get fog on the lake that surprises you, this is where Radar would be more helpful.
I would think that one of the new FLIR night vision cameras would be of more use on the lake, but I don't have one, and the field of view was pretty narrow for the one that I did briefly see in action. They can cost about the same as Radar.
With this being said, I'm a bit of a technology geek, so when I update my electronics, I'll probably also update to the newer solid state doppler Radar also. But I really would like to experiment with the FLIR thermal night vision to see if that's more useful.