Without wanting to look like a boots salesman, several reasons why I think that their glycerin and rosewater is a good choice for a spironolactone vector:
1) Glycerin is a very good solvent; many things dissolve better in a glycerin/alcohol mix than in alcohols alone.
2) It is a moisturiser, which helps to counteract the drying effects of e.g. nizoral.
3) It contains boric acid, and a low pH is meant to be good for spironolactone stability.
4) It smells less than other stuff I experimented with.
5) It is cheap ~£2
One thing I will say against it, however, is that it takes some time to dry, about the same if not longer than rogain/kirkland minoxidil, though I suppose this is partly attributable to the moisturising effects.