They are definitely hard to read but once you get past the mystery of them, I have found that it really comes down to the ISTP themself. Some of them are fine and some of them drain me. My current bf is an ISTP and he is fine for me to be around long term, others have been great for me to be friends with…. I.E. my ENTP friend’s husband is also an ISTP, however, he has anger issues so sometimes I really don’t enjoy the way he speaks to her (he can be pretty cold and cruel when he’s in pain, hangry, or tired) but he is great as a friend because he would bend over backwards whenever I need his help and I enjoy watching him put together things and tear them apart, he’s stubborn in the fact that he has major control issues so he won’t let me or anyone else help him and wants to do everything himself which gets rather annoying sometimes, and others I wouldn’t want a friendship with at all because a couple of the ones I have come across are way too self absorbed, so again, just depends on the ISTP in question. I don’t know or understand Enneagrams yet so I can’t help you with that part of your question, I’m just going by personal experience on the ones that I have met.
I think ISTPs and INFJs in general find each other hard work after a while in close friendships and relationships, though as always there will be exceptions. Dominant introverted intuition and sensing are very different sorts of motherboard and neither of us can have a real inner feel for the other.
