You'll remember cetearyl alcohol is a fatty alcohol that boosts the substantivity of a cationic ingredient, like the PEG-3. Polysorbate 60 is a high HLB emulsifier, so it's included to help emulsify your conditioner into water, because normally a cationic quat is an oil soluble only product. It will also thicken your conditioner so it's not a thin, watery liquid (like you'd get with cetrimonium chloride alone).
The PEG part in PEG-3 (etc.) means it has be ethoxylated to become a PEG ester and it's been quaternized to be positively charged (cationic). This is the key conditioning ingredient in OSC.
This is a diakyl quat - a quaternized diamido amine. The diakyl quat part is important - the more hydrophobic (water hating) the conditioning agent is, the more substantive it will be to your hair. Mono-alkyls (like cetrimonium chloride) are lightly conditioning, diakyl quats will be offer medium conditioning.
It is an emulsifier, so you can include oils and butters in your conditioner (and you can use it as the emulsifier for a lotion - see recipe below). It is meant as a "one step conditioner", so the formulas you will find generally call for 4 to 6%, meaning you're getting 1 to 1.25% PEG-3 (etc.) as the active ingredient.
So what does this all mean? Incroquat OSC seems very similar to Incroquat CR. It's a good conditioner on its own and makes "economy" conditioners, but I don't know if you'd want to use it alone. I'd want to use it as a secondary conditioner with something like BTMS or cetab as the main conditioner. It's going to increase the viscosity of your conditioner - as all cationic quaternary compounds with fatty alcohols included will do - and it's going to offer conditioning to your hair.
So why use this over another conditioner? (In the spirit of complete disclosure, I've never used it, so I can't tell you what it feels like...if anyone wants to send me a sample, I'll make up a few formulas!)
It's inexpensive, like Incroquat CR, and it can be used with minimal additions. A pound was $5.00 at Southern Soapers, compared to $7 a pound for CR, and $15 for BTMS. (Or in Canada, up to $25 per pound!) If you are making tons of conditioner and selling it, cost may be a consideration.
Although, given that you are using a maximum of 7 grams per 100 grams of product, and 100 grams of product should last you a month, you should be able to get 65 - 100 gram bottles of conditioner from 1 pound of conditioning emulsifier.
It can also be used cold - you would melt your OSC with 25% of the water phase, then let it cool, then add the rest of the ingredients. (Having said this, I find it quite easy to create a conditioner with an all warm phase, so again I'm not sure how this is a benefit. What do you think?)
It is intended to be used with minimal additions like oils or silicones. Most of the formulas I've seen use 4% to 6%, maybe 2% of a hydrolyzed protein, preservative, and water. That's it.
And some people really like to use the PEG-3 Distearoylamidoethylmonium Methosulfate. It's found in a lot of commercial conditioners - St. Ives, for example - and it is a good conditioning agent.
Here are a few links if you're interested in learning more about Incroquat OSC...