I think we all agree that the switch is not user friendly. Here are the steps I use when working with the DF-500;
1- Mark your board, set up the depth/fence and cutter to be used,
2- Hold vertically the DF-500 away from the board and move forward the switch (make sure you apply force ONLY on the tip of your thumb),
3- Align the machine against your mark and hold firmly on the board,
4- Push gently* on the machine (I have my hand midway on the plug-it cord),
5- Push back slowly** and give a 2 seconds to the CT-Vac to evacuate the dust,
6- Leave the machine running between mortises.
Compare to a biscuit jointer, this is a precision tool. To reach a maximum of precision, take your time.
*With a harder wood, slow the penetration movement.
**More or less but give the vac the time to suck that saw dust.
The DF-500 is a fantastic tool and like any tool it requires practice.
Good luck