Might be an oddly specific post, but I've seen this recommended, and I'm just not sure I understand how it would be used effectively. Surely an air/water kineticist should be acting as a ranged spellcaster most of the time, in other words, not being within 10 feet of an enemy and especially not of multiple enemies. Furthermore, this impulse doesn't discriminate, so even if you were within 10 feet of all your enemies, you'd probably be within 10 feet of your allies too, subjecting them to a bunch of slippery bullshit as well.
Am I missing something about what makes this useful / not a detriment?
Aha, that's one thing I overlooked. It would help for sure. It still doesn't solve the fundamental problem, though, that I feel like despite being a CON based class, an air/water kineticist probably is trying to avoid being within 10ft of the enemy.
It's a really strong effect and it requires some really careful positioning to work well.
Using Weapon Infusion to give reach to your melee strikes helps in staying at a range to be far enough away from your allies to keep from wrecking them as well as Air's tools for mobility (Four Winds, its Impulse Junction, Lightning Dash) to get your positioning exactly right (the water-air kineticist I'm playing is also an Elf with Nimble Elf and Fleet). Tidal Hands and the Water Impulse Junction allow you to push enemies if they get too in your face, which can save your taking a move action and keep enemies at the ideal spot for your aura.
Your frontliners without reach will probably be taking lots of hits just because threats will have to Balance over to you, but in case they do, you'll want to have your Dexterity as your second stat to maximize utility from your light armor to deal with threats and to bolster your Reflex saves. Water's Ocean's Balm and Deflecting Wave feats help with healing and negating damage outright respectively, though I'm skipping Ocean's Balm in my build. If you have Free Archetype, you can go Rogue to get Nimble Dodge against attacks that Deflecting Wave won't cover and Mobility to make your Air Impulse Junction and other incidental positioning bulletproof.
The object in a lot of combats is to use your mobility options to get far enough behind enemy lines to cause havoc with the aura while still being a move action away from your targets. Getting a Slow from a critical hit with an Elemental Blast in the aura also helps eat up actions that would otherwise be used to hit you.
Even if you don't want to be in the mix actively debuffing with your aura and you want to be ranged, the Balance clause makes the aura function as a very strong deterrent zone. Balance requires that you be on uneven terrain to do it, meaning that an opponent outside your aura without reach would need to Stride to the square inside your aura and then use the Balance action to make it the last 5 feet without falling. It's now spent two actions just to get to you and it's off-guard for having taken all that trouble.
I haven't played with it a lot, and you can imagine lots of places where it won't be the best option like profoundly close quarters combat, but the Kineticist has some other tools to deal with those situations too (the options you've already noted that don't synergize with Winter Sleet). It's a truly great option where it's great, and an own-goal when it's not, but making tactical calls is the name of the game. On balance (haha), I'm a big fan.
Update: it's also worded so that if you get an opponent prone in your aura, they can't get back up. Standing is a non-Balance move action, which would render them prone again.
But the aura is 10ft. Or 20ft with a feat, which still doesn't get you outside a movement action. How does that work?
Aura Shaper is a mid-tier feat that can expand the size of the aura to up to 30 feet, but earlier, you're trying start a fight by activating your aura and move to something like this
where _ is a blank space, X is your opponents, O is your allies, and 👨🚒 is you. Your group of allies is clustered to the left of O, and your group of enemies is clustered around the right side of the map, that is, around you, but you're in a spot that has a blank space between you and any of them as well.
Keep your friends far and your enemies close-but-not-that-close, as the proverb goes. You can then use Air and Water Impulse Junctions to keep your action-taxing distance from foes intact when they approach.
As the fight goes on, positioning changes because your allies and enemies get a bit more intermingled, but those position changes are extremely costly for your foes (a decent chance of falling, no chance to avoid reactions because no Step) and free for you (Air Impulse Junction, Water Junction).
It's 20 feet. At 10. Only becomes 25 and 30 at levels 15-20.
As for the chart, honestly that just looks like you're a light armor caster asking to be flanked and annihilated. The enemy on the left can simply step over to you, and honestly who cares if it falls? Flanking will counteract the attack penalty from being prone. If there are even 1 or 2 more enemies not represented here, this caster in the enemy backline is surely in trouble.
I don't think you're a light armor caster:
On the diagram: the enemy on the left can't Step. It has to Balance, forcing two possible Attacks of Opportunity and a chance to fall prone where it is and end its turn. Will it do all that just to set up a flank on you for its allies (that only have a single action to Strike when they get to you from outside your aura)--when you're going to get a completely free non-provoking move next turn anyway?
If it does, I'll take that deal.
I missed Balance being a separate action entirely. Okay, never mind, I understand now. Balance being a completely separate action required to not-even-safely move around in the aura is the key I was missing.