Actually, I have not seen any substantive materials that suggest that bilge keels (twin keels) are more stable. On the contrary, for a given hull shape and amount of ballast they tend to be less stable as half of the combined ballast weight of the keels is generally to leeward of the center of bouyancy when heeled.
Based on my own experience working at and sailing on a rental and sailing school fleet that included bilge keel and fin keel versions of otherwise identical Westerlys, my observations from jumping back and forth between these otherwise identical Westerly''s and watching them under sail over a summer, clearly showed that the bilge keel versions were slower, made more leeway and were more tender than the fin keel versions. Obviously this is a small sampling but my observations were pretty much in keeping with the literature that I have seen on this subject.
One other point to be aware of, once aground with a twin keel boat you are seriously aground. There is no heeling one out or twisting one off a grounding. You are seriously aground where a fin or even long keel can be broken out.