I installed them when I did the engine work on my Evo. Install was easy, can't say how well they work though, as I didn't have noise from there to begin with.
All the rocker lockers do, is prevent the shaft that the rocker arms are on from rotating and banging on the mount bolt. If you have noise from the rocker shaft banging on the mount bolt, you'll notice it will be quiet. If your shafts aren't banging, you probably won't notice any difference.
That said, they're not a bad thing to install, absolutely will not hurt anything, and it's not hard to do. They're also not terribly expensive. Another good thing about having them is if you do develop valve train noise, that's one less possibility of where the noise could be coming from.
The only down side is that you have to pull them out to pull the shaft if you ever need new rocker arms, or if your rocker endplay gets to be too much, etc. But how often do you really need to change the rocker arms or have to pull those shafts out?