Behaves the same as the LA-2A, you've got the "in your face" sound. If your vocal is harsh, then it can fix it, gets it smoother and softer.
Changing the tubes can be a good development, the originals sound weak.
Warm Audio puts the Pre-Emphasis potentiometer on the back of their unit... On the KT-2A I often adjust it, I'd put a cap on it :)
You have to send +24dB audio signal to its input to really drive it. Below that you get a weak sound...
If you want an LA-2A, buy an LA-2A. If you want something that works the same way as the LA-2A, I recommend the KT-2A. I've never used a Warm Audio, but I'm satisfied with this product. High quality, low price. Planning to buy another one to link them stereo!