Its also worth noting in the countering spirits buffing category. that Anyone with the counterspelling skill which includes Mystic adepts and some spirits can try and counter the spell. I will also point out that if your having the spirit cast the spells then you are only getting the spirits casting dice pool and it is suffering sustaining penalties so if your using it to cast 2 different spells the 2nd one cast will have a -2 applied to the casting check because its already sustaining one spell. And then from that point on its at -4 to all of its actions if you decide to have it do anything besides sit at home and sustain those buffs for you. Now i am not saying its not powerful and very useful way to apply your spirits but it does have some inherent limitations. Another thing to think about is wards, if the mage encounters any wards while using this strategy he now has to deal directly with the ward to keep his spells. This is important because its hard to deal with any kind of ward quietly unless your have invested in some very specific meta magics. For a normal mage the ward is a minor inconvenience as he can simply dismiss his spells, turn off foci and stop any astral activity and then walk through the ward without tripping the alarm. If your using the spirit sustain method you have to have your spirit stop sustaining the spells, do everything else, walk through the ward, then call your spirit back burn up 2 more services to have him recast the spells and then send him back to. Its not massively problematic except for wards can crank up the service cost overhead a bit.