I have had it for 2.5 years, initially I bought it mainly for the batteries since I found it on sale. Eventually, even though I use it for amateur use, I have used it extensively.
1. The tool does not have speed adjustment. It operates at 26000 RPM (without load, I don't know exactly how much it drops with load, the 25000 mentioned by some in the description may be a good approximation). This means that in order to achieve the correct (linear) contact speed of the tool (e.g. burr) with the material you want to work on, you need to pay attention to the diameter of the burr you will use. For example, if you want to work on aluminum (Fine machining low stock removal) with a Karnasch HP-7 burr, Karnasch recommends a cutting speed of 900-1100m/min. With 26000 RPM, this corresponds to diameters of 11.03mm-13.47mm, and you need to choose a diameter of 12 (or even 10) and you're good, but for example a diameter of 2mm will not cut properly. On the other hand, if you choose and buy burrs for 2-3 materials/jobs, then you just put them on and you know they work without having to search for the right speed to set.
2. The chuck (collet) is 6mm. I have found and bought 3mm and 8mm chucks, but I wanted to use a Dremel speedclick on it, which requires a 3.2mm chuck. It does exist, but I couldn't find it in Greece (I didn't order it from abroad).
3. Be careful because it is powerful, at one point when I was cutting some iron because the base where the bottle rests on in the trunk had broken, the burr came off (definitely my mistake) and I didn't even hear it fall. You don't want it to hit your eye or forehead, etc.
4. Well, the tool is great.