Hi Lara
I have not used Dermatch but do use Toppik and Nanogen on my thinning crown with excellent results.You are right that they thicken the hair shaft as they are electrically charged or whatever and this makes it hold on the hair and not much will drop to the scalp.
Unfortunately if you run your fingers through it,it will rub off like you mention with Dermatch.As Jobi says apply some hairspray to provide a coating over the top which will help protect if it rains etc.
If you do get lucky on a date ,try not to let them run their fingers through your hair and dont lay your head on their nice clean pillows.
Hope this helps.