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Alan, much depends on what one's purpose for a "paint thinner" may be, in terms of oil painting. Solvents, (regardless of their composition) ultimately destroy the binding character of vehicle oils and resins by over-extending them, rather like a rubber band ultimately fails when over-extended.
"Isoparaffin based" is a fancy-schmantzy way of saying the solvent is a petroleum distillate. In other words, it's mineral spirits. Mineral spirits is basically refined kerosene. For use cleaning brushes and tools, kerosene is superior to mineral spirits, because it is more penetrating, and with a lower vapor pressure, less is emitted into the air. Odorless varieties of mineral spirits are not necessarily "safer" for the atmosphere just because you can't smell it.
Back to oil paint, pure gum spirits of turpentine is no more nor less toxic or "unsafe" in the studio environment than mineral spirits. Resin varnishes (including mastic, damar and copal) cannot be satisfactorily compounded with mineral spirits, because the petroleum product causes varnishes to be cloudy. As a solvent component of mediums, turpentine provides a different chemistry which promotes interior drying of paint films. In the main, a painter's use of any solvent is (or should be) so minute as to be less than problematic in terms of air quality safety. In all cases, the studio environment should always provide ample ventilation and fresh-air exchange.
The toxicity of turpentine has become a "hot issue" in some circles. This is probably due to the current prevalence of solvents touted as "turpentine" which are NOT pure gum spirits of turpentine. The last few years, most "turpentine" has been bulk-manufactured in the far east by steam-distilling forest wastes of indiscriminate species. Stumps, limbs, roots and slash are ground into a pulp which is cooked to yield a distillate solvent which reeks of creosote, and a number of active terpene toxins. It has no use in the studio for any purpose.
Good turpentine is the gum exude of certain conifers, tapped from living trees. The spirits of pure gum turpentine are the distillate. Rosin, colophony, and spirits of turpentine result from the process. Good turpentine smells clean, like a pine forest after a rain. That it is not necessarily "toxic" is proven by its long duration as a staple in liniments and cosmetics.
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