With some there's the ability to be brutally harsh to others with very high sensitivity to criticism themselves, anger is often present and emotion tends to be more reactive and explosive than other types. Jealousy and insecurity in relationships also seems more common [refer to my thread on Jealousy to understand why I have an issue with that ].
Their passion is something I love, the intensity makes me cautious though. I'm fine with impulsiveness but unpredictability in emotions that may be formal one moment then explode as anger or volatility without warning doesn't gel with me, I can't trust that in people, it activates my defences. As we're talking in the context of a romantic relationship, that's clearly a bad thing.
There are 3 Enneagram types in particular that I find dom sx's easier to connect with though:
5s have a strong need for independence more than most others so they don't bring out a claustrophobic feeling in me, they also push and pull with their boundaries which can give me some breathing space (although it can also leave me unsure of where I stand). 5 sx's don't appear as passionate or intense to me until you hit on a topic that they care deeply about. Anger can still present but I find 5s more disconnected and even than other sx's. Their intense emotions often come out as more depressive than volatile. Basically they seem more consistent.
7 sx's don't tend to cause any concern, maybe it's because of the shared enneagram, maybe because their moods tend to display more as excitement, happiness and other positive expressions which I love and am magnetised towards. Maybe both.
9s are also generally not too intense for me, if we were to use Tritype 9w8 would be my second type, I can relate to their style quite well and I tend to find them inoffensive and happy-go-lucky most of the time. As with 5s their ability to withdraw makes it easier for me to get the space I need.
This is of course all generalised to give you a global view of my take, there are always exceptions.