All things considered this a a very nice mixer for the price and, thus far, all features except the tuning oscillator work as expected.
About the tuning oscillator... it is the most unstable osc I've yet to encounter so I can't fathom how it's intended function was for tuning purposes. It seems to have been designed/manufactured without any PTC resistors or other temperature compensation at all (similar to the issue with the first batch of 112 Dual VCO modules). You can turn the unit on and let it warm up and calibrate the tuning osc using the trim pot on the back to a perfect 440Hz (or 220/880Hz) and you'll be lucky if it stays calibrated for 30 seconds. Turn the osc off via the on/off frequency selector switch for even a few seconds and then back on and it will be out of calibration by 15-20 cents. Try to get around that by calibrating it and just leaving it on all the time and using its mix volume to bring it up when you need it? That doesn't work either as it will drift out of calibration 10-15 cents in 30 minutes to an hour.
It's a minor annoyance and not a reason to keep away from purchasing this mixer as a lot of people probably use a different tuner anyway, but if you're going to take up space on a module with a feature that you list as a selling point, it would be nice if it worked reliably.
I did open a support ticket with Behringer on this asking if this was a known issue and, if so, was there a fix for it. Their response was a canned 'If you feel your unit requires service please contact one of our authorized repair centers...' not very helpful at all in that regard.
