That Gastester is a great tool. I couldn't find anyone who would set the idle mixture per the BMW CO spec of 1.5% for less than $125 and an hour on a dyno.
Bought mine from the U.K. for $129 shipped. This posting is an even better deal.
The CO pot on my RS was off by about 5% too rich. My K75RT was about 3% too rich. Was getting black plugs before, now they are reading correct, nice and tan. Couldn't have gotten the mixture correct as easily without it. The alternative was to make an adjustment take a plug reading, repeat, repeat, repeat...