They are brighter when the wiring works. They light up more of the unit, but definitely do not dim with the rheostat, as buckaroo was saying.
If your lighting is almost non-existent right now, they may not make much of a difference until you find out why. One common reason is lack of sufficient grounding between the socket and cluster, cluster and dash, and dash with body.
The other is something wrong with either the wiring (less likely) or the light switch and it's connector (more likely). But grounding is most likely of all for most of us.
Have several customers here locally that are using them and in each case the lights are brighter and more even. None seem to mind that they don't dim though. I thought that would be an issue, but so far they like them too much.
The two guys using the blue lights absolutely love them. One has a Blue Bronco, and the other has a White one.
Tried them in a Red EB just for S&G's and they looked like crap. He went with white and they look fine.
The only real complaint I've had is that the high-beam indicator replacement lamp has a blue light, while the lens over it is red. Makes for a bitchin' hot-rod Mooneyes Purple look and it dims it down a bit.
I like it a lot, but some say they don't care for it.
Paul