General rule of thumb; don't summon a demon with a higher Essence score than you.
This is generally easy with Demon of the First Circle, and not hard with Demon of the Second. First Circle Demons are going to be unusually potent if they hit E4, while most Second Circles aren't going beyond E6, with most at E4 or E5, both Essence scores a player could reach in general (if extended) play. At the same time, Second Circles aren't going to have anywhere near the same level of anti Summoning defenses as Demons of the Third Circle, and even if they have some, Demon of the Second Circle is the sort of spell you spend a month preparing for and involves you dumping a lot of motes on debuffing the demon in question and keeping a combat specced Celestial close at hand just in case things go wrong and you roll all ones while their chance die comes up with a ten.
Demon of the Third Circle though?
Demon of the Third Circle is the Summoning spell that, like much Adamant Circle Sorcery, demonstrates 'can' does not equal 'should' or 'is a good idea.' Because you can reach it at Essence 5. And at Essence 5, the demons you'd likely be interested in Summoning probably have the kind of dicepools where, debuffed as much as you can, they have dice parity with you.
That's not a big problem with a First or even Second Circle Demon, if you have the right precautions.
Third Circles aren't First or Second Circle Demons. First Circles are tools, even if they are living, sapient things. Second Circle Demons are buildings that would define an entire city's character, weapons that destroy armies or merchants that trade in the dreams of their lessers. Not so Third Circle Demons. These are the beings that would define what an entire Direction of Creation is known for, a city palace of debauchery, a chasm that swallows the betrayers, a roaming shadow of music that twists those that hear and see it, a plague of melancholy or the baleful gaze of a green sun that will take no peace.
In the First Age, a skilled team of mortals could bring down a First Circle, and expect injuries but no deaths. In the First Age, Dragonblooded could fight Second Circle Demons. Not safely, perhaps, but as equals. In the First Age, a Third Circle toed the line for a united host would bring it low, even if a few of Creation's greatest defenders might fall in battle.
This is not the First Age. This is the Second Age, much diminished. If mortals face a First Circle, no matter how well trained and well equipped, they won't keep up, and with the poor medicine now available there will be a few permanently crippled at the end of the fight, or rather more likely, dead and dying. The Dragonblooded are not what they used to be, much of their equipment lost to the ravages of time and war and what remains carefully hoarded, but a Sworn Brotherhood can still lay Second Circle Demons low, if at a cost.
But Third Circles? In this fallen age, there is no united Host. In this fallen Age there are no Lunars ready to jump into the fray to stall the Demon while a team of Solars prepare. There is no Sidereal to spin the threads of Fate so that the demon is entangled while mortals can flee from the conflict safely. And there's no Solar master combatant ready to bring the hurt.
In the Second Age, a Third Circle on the loose is the sort of thing that ruins nations, and there's no one left to pick up the pieces.