In a recent session, at start of day, my PC mage and another PC mage each summon a spirit, as they probably do just after almost every sunrise and sunset. I roll reasonably well and get my F5 Spirit with a few services. (I forget which kind of spirit, but Spirit of Man with Combat Sense is kinda default, so that it can buff me and Sustain the spell all day long; avoiding surprise is a good general thing to have during downtime.) The other player rolls badly and/or the spirit roll is high, so his PC ends up not getting any services. Maybe the spirit says "Don't bother me, I got things to do!" Player tries again and again the spirit dice (Force) get more hits than the mage dice (Magic + Summoning). At that point I say, in character, "May I help you with that?" The other player glares, his PC presumably glares, player rolls more dice, and his mage finally gets a spirit to agree to do him some services.

So... do your PC mages do their downtime summoning and binding on their own, or do they use the Teamwork rules? Yet another advantage to having buddies or a full cabal, rather than working solo! ¥1500 to bind an F3 Spirit with an optional power is a worthwhile deal, but if you get several mages together to max out the DP for the Binding test, and bind, say, 10+ services, it can become a much, much better deal. (Binding an F3 Water spirit with Guard: ¥1500. Not drowning when the boat capsizes: priceless.)

That's in addition to the benefit of having someone on hand to save you from getting killed if the spirit's roll hits on every die, the conjurer passes out from Drain, and the spirit is bloodthirsty. Bare is back without brother to guard it, and all that.

That's an interesting idea. Somewhat open to abuse in magic-heavy groups, though given that the Summoning mage still has to suck up the Drain, you can't really overdo the Force, you just generally get more services. I'd say the magicians would have to share the same tradition: shamanic rapture and hermetic analysis don't mix well, in my view of the cosmology.

I won't be allowing Ritual Conjuring, or even teamwork tests for Summoning anytime soon in my games.

In addition, I think both magicians should have to resist the Drain at full, so you can't have a weak mage with strong summoning just to help out the strong mage with weak summoning, cos they'll blow their brains out.