Don't have much recent experience, but from what I recall from dating an ISFP years ago:
- ISFPs tend to be more present in the now, so can be helpful for INFPs (who can be so future-focused they miss the good stuff while it is happening).
- ISFPs are even better at rationalizing than we INFPs... can be scary to see in action.
- ISFPs are attuned to emotional nuance... makes for a great Fi connection and a sense of being understood emotionally.
- ISFPs tend to be less tuned into theorizing and abstract arguments, so one can feel a little lonely intellectually, depending on how much your interests overlap.
I ended having to be the "adult" with the ISFP I dated, so had to be the one to keep track of time, expenses, commitments and other practicalities; however, that could have been more about the individuals involved than type generalities.
If my monologues tended to wander off into the abstract and theoretical, he could go into great detail about options and details about his hands-on projects. We were perfectly capable of boring each others with our interests (and how we talked about them) if we weren't careful.
Still the physical and emotional connection was great. Also his hands-on "jump in and figure it out" approach was handy on occasion. I'd want to read up and prepare before I tried something, while he was more willing to jump in and figure it out himself.
I'd say it can make for a great relationship, but does mean someone has to be willing shoulder the practicalities despite it not being a natural strength.
The ISFP I dated (and still know) definitely struggled with school. He had severe test anxiety, and basically gave up on education by the time he reached high school. He managed to drift through high school and graduate, but had definitely checked out long before. He also has had a hard time finding a job (or career) that was both fulfilling and paid enough to live (not that that's an uncommon problem).