I have two of them. They are fairly decent, but I've had a long history with them since they were first released, and they are not without issues and cautions.
The first one I got vibrated and was very loud. The problem is in the bearings. The motor itself has two small ball bearings, which is good. There is a large ball bearing at the end of the collet/chuck that bears the brunt of the loading against the shaft. It's this bearing that seems to be the problem. If you were to unbox a half dozen new rotary tools and start them up, each one will likely sound different. Like my first one, the bearing sounded as if it was damaged when pressed on the shaft, perhaps the pressing load was applied to the outer race. Loud whirring sound that got worse as I used the tool. In a couple months, the bearing began binding and self destructing. I exchanged that tool for a new one, which was much quieter. It soon became totally silent after it unexpectedly stopped working. Another exchange, this one was louder than the second, but nowhere near that of the first. I was mostly happy, until I was using it with one of the larger fiber cutoff wheels like those supplied with the tool. I had the tool set about midway in speed, and the wheel bound tight in the cut (my fault). But rather that shut down from overload like my cordless Dremels, the magic smoke escaped from the Milwaukee immediately. I took this one to the local Milwaukee service center and they exchanged it for a new one, kinda hinting to me that these WILL burn out if stalled. I took this new tool home and decided to treat it very carefully, no hard work, etc. When I tried it out for the first time, I was amazed at how quiet it was. At low speeds it sounded like an old aircraft gyro, a very quiet whirring, and ZERO vibration. Even at the highest speed with no bit, the tool was half as loud as the previous ones, and no vibration. I figured they finally got the knack of production and/or found better bearings. I bought a second from the Milwaukee store. Unfortunately, that one was not anywhere near as quiet as the other one (it sounded like the bearing was damaged during assembly, or was not as high a grade of bearing), but there was not a lot of actual vibration except at the highest peed, but was at least tolerable.
In short, these are the only Milwaukee tools I have encountered problems with. They could still be damaged by locking up the tool at higher speeds, and the quality is definitely rather variable. I use the super smooth one for precision work with small bits, and the other gets more "normal" usage. For being cordless, they have as much power, if not more, than my old corded Dremels, and have a 30,000rpm top speed. As for coNsistent quality, YMMV.
