The boots one is slightly purer but more expensive and is also thicker so its good but may take a little longer to steep. the Lucemill or lubrisolve is better for mixing, better priced and won't make a difference healthwise etc, most people who mix buy their Vg from places like those i mentioned. My last 5 litres where from darrant and the one before that lubrisolve. i think the lubrisolve is 99.8% not much of a difference. the main thing to look for is USP or EP grade thats the main thing as it means its pharmacutical grade, food grade is probably ok but with Pharmacutical grade you are safer.
