I've used the 700 to mortise Ipe, one of the hardest woods in the world. It's even cut mortises into Ipe end grain.
I found the a too fast plunge rate will produce a mortise with one end slightly higher than the other end. Seems to be like a router's climb cut.
I have also encountered a problem where a series of mortises were individually correct, but were at different distances from the reference surface (top of the board being mortised). In one case, the Domino fence had shifted very slightly as I cut the series of mortises. The last mortise was significantly higher than the first. I didn't have the fence tightened adequately. In the other case, the bottom of the Domino was contacting my workbench. I didn't have the board being mortised high enough off the bench. So, the reference surface was the work bench and not the top of the board being mortised.
Senaca sells aftermarket screw-on plates that eliminate the need to use the Domino fence and produce level mortises. Woodpeckers has also announced a similar product. The Senaca product is cheaper and works very well.