When considering small scale operations, with the least possible investment in equipment, and the greatest possible safety margin, I look at GRAS solvents (Generally Regarded As Safe). That leads me to Propane, Butane, and Ethanol.
To perform museum quality extractions with Propane and Butane, requires addressing Mystery Oil, which means Reagent grade Propane and/or Butane blends, or the equipment to pre-distill the LPG before extracting with it.
It also presents one of the highest hazard indexes of all the extraction methods, because of its high flammability and explosive potential, especially when open blasting to minimize investment in equipment.
Given the rash of residential explosions legislators are also trying to get a handle on and I predict closer scrutiny and control of all forms of LPG.
190 Proof ethanol is not cheap because of tax burden, but works right out of the jug and isn't pernicious if the residuals are above the 5000 ppm limits for FDA Class III solvents.
As the human sensory threshold is significantly below 5000ppm, you can detect its presence by simple taste and smell, even if you don't have a Gas Chromatograph.
It is a polar solvent, so not nearly as forgiving as LPG when it comes to things like water, water solubles, and C-55 chlorophyll, but more effective extracting C-22 polar carboxylic acids and less prone to extract beige C-30 non polar plant waxes, C-40 yellow/red beta carotene, and C-55 olive brown pheophytin.
Freezing to tie up the water and water solubles ostensibly reduces C-15 flavonoid pickup, because they are water soluble, but also ties up the chlorophyll and pheophytin locked in by frozen water soluble chlorophyll binding proteins.
My first cannabis extraction was Green Lizard, followed by refluxed chlorophyll soup, followed by refluxing bubble, followed by BHO open blasting. I subsequently picked up QWET as a way to get a higher yield for formulating chlorophyll free cancer meds, but when vaporizing became popular it was a natural.
Here are some shots of my first QWET extraction before removing the alcohol.