I have a Domino 700 XL and the Seneca Small Mortise kit. Plus the 4, 5, and 6mm 500 bits and matching sized dominos.
Overall I have been happy with this combination and have used it on 3/4" and 1/2" plywood. I have used the 8mm bit in 3/4" plywood without any issues, but it is on the big side. I have also used the 6mm bit and dominos on 3/4" plywood.
One issue I have had with this setup is the preset depth of the mortice doesn't match the domino when using a shallow depth mortice using the 500 bits in the face of a board. I solved this by making a spacer out of PVC tubing. This is described in the 500 supplemental manual, but works fine for the 700 XL. Took a while to get the right length, but works fine. I talked to Ryan at Seneca who suggested this idea. Great support from Seneca.
The other issue I have is that the support bracket is small when using the 700 on the face of a board. It works, but feels precarious, not much to hold onto. I plan to see if I can make a fixture that is bigger with a handle to make this a more secure operation. Has anyone else done this?
I hope this is helpful.