I was scary for the conflicts that would arise, but I haven't experienced them yet.
I've had a brief relationships with ISFP women. It starts easely, because of the same temperament, but probably even more because of the seemingly Ideal partner.
Although I recently saw in a threat Strnggg (INFP) and Cyclops (ISTP) have a big fight, they are superego too... so I guess the fights can be pretty mean.
But so far for me personally, superego relations are fine. Yet the socionics descriptions still scares me enough not to look for another superego girlfriend.
BTW now I remember a particular trait of this relationship which stood out. One partner is too clingy. In my case the ISFP women was way to clingy. Also the reason I broke the relationship. I've had this similar experience with an male ISFP aquantance of mine. They both kept page messaging me for a year... after I broke contact.