I have purchased a lot from SOS. They were the first FO company I discovered. If you order anything other than Extreme you will be using oil diluted with a carrier (most likely IPM) and I do wonder if even their Extreme Oils are somewhat diluted as they claim you can use them at a concentration of 2 parts FO to 1 part carrier as a perfume!
I have replaced most of my FOs from them with cheaper/better versions from (mainly) Nature's Garden, Sweet Cakes, Wholesale Supplies Plus and Fragrance Buddy. SOS does have some FOs that nobody else carries though so I am still a customer...they also have some really good designer dupes (and some really bad ones LOL).