In order for a silicone oil to be functional and qualitatively valid, it must be pure in terms of the raw material used, only in this way can it express all its incredible functionality.
There are several families of silicone oils, depending on the chemical structure that forms and differentiates each of its components: a structure formed by a linear chain of silicon and oxygen, for example, will make the silicone oil very stable to oxidation, giving it a high flash point and a low solidification point.
A different silicone oil may perhaps have a wider operating temperature range, and yet another one may be more compatible with plastics and elastomers: the quality of the oil must always be judged on the basis of your needs.