I've had the Trackmaster for a few weeks, so am happy to share my views but bear in mind I'm a newbie. I use it for female vox. I'm very pleased with it, and comments on something I posted recently mostly mentioned how good she sounded, so there's a pointer.
I've tried my bass thorugh it and it was absolutely horrible - I couldn't get anything that sounded even vaguely usable.
One thing is that, as already mentioned, its controls are aimed at musicians who just want to get a good sound without doing any technical stuff. So, there are only two compressions ratioes; 3:1 and 6:1 (the latter is selected by pushing a button marked "tight"). There is also a button marked "punch", which apparently restores the loss of definition caused by a fast attack time. (We can guess how it works but the manual doesn't tell you).
The knob marked "compression" is actually used for setting the threshold.
The three band EQ has high and low shelves, (low shelf range being selectable by an instrument / vocal toggle) and a mid-band called "Presence" which boosts at 1500hz. You can switch the EQ to be pre or post compression.
Finally the tube knob adds a bit of warmth which is quite pleasant.
Overall, it strikes me as good value, great for a beginner like me, very useful for live situations, letting you quickly adjust vocal sound to a new venue, but for serious recording by grown ups its compression ratios are too harsh and it offer insufficient control.
Hope that helps
Garry