Mclube/Sailcoat is a teflon based product, not silicone as posted earlier.
Yes it is expensive. for a 350 ft^2 spinnaker I use about 1 quart of it. I use a pump sprayer and put on an even coat. figure around 30-50$ per spinnaker. I also coat the snuffer bag and hoop heavily. Personaly I think it is money well spent. I have not tried any of the silicone spray products.
When your figure the cost of a chute is 900-1000$, the sailcoat is cheap and reduces wear on the chute

Eric