I do both, but I usually GM more than play. I was suggesting a d6 rule or similar to control this power, but I would not have any problem with a player doing that. If a player wants to risk her life and use portal to summon a demon, it’s up to her and it is none of my business.
And I don’t see a problem with binding demons, it needs both willpower points and successful rolls, at some point it will fail and the demon will pay back all their “kindness”. You can find demons just by travelling, why would summon one be too outstanding?
But you as a GM have the last word and if you don’t like it, do not allow it. Using portals for travelling should have a risk. Using portals to summon demons should not always work.