I have this device for 1,5 year now. I have used it for recording vocals, drumkit overheads, percussion microphones.
First of all, the clarity of the SPL Goldmike 9844 is very good. It provides a clean boost, esp. necessary for dynamic microphones such as Shure SM 7. Using it as an additional preamp for condenser mic (I have tried, for example, Mojave 301 FET) is mostly not necessary as the mic is already quite sensitive, preamps on the mixer were enough in my case. In another scenario, I was recording percussion with a pair of Aston Starlights, got crispy and clear sound with the preamp.
Regarding controls, the FLAIR button is useless. It is a preset equalization and I did not find application for that.
Now the cons. SPL Goldmike 9844 is very-very-very picky to the power network interference. I had noise problems, which I tried to figure out with Thomann (thanks for the awesome support as always!). I have tried Furman M-10x E. Did not work. In the end, I run the preamp through the UPS + a custom network filter after it. That reduced noise by 20-30 db and kept it on a tolerable level. I have recently discovered that the noise was simply from the powerline connector (Ethernet over power network). If you are buying this device you have to make sure, that your power network is flawless, otherwise you will have LOTS of noise in the recording.