I have used my PC 89x router under my RT very successfully and have found that it works very well - with a few common common sense items.
Be sure that you do not go back and forth with router height adjustment. - I make sure that when I am adjusting height, that if I have to adjust down, that I adjust quite a bit lower and make the final adjustment going in the UP direction to make sure that any backlash is taken out when adjustment is complete.
Make sure that the locking band adjustment is not too loose, as this may cause variations when the router is then locked in place.
Other than those, I have it very usable and quite reliable.