Blu-Tak is cheap, and also not a very good material sonically, having resonance issues that affect linearity and cause other sonic anomalies. In the case of "try it and report back," our customers have "been there, done that" repeatedly over the years, consistently finding Fat Dots to be a better option with speaker stands, and also a worthwhile upgrade from Sobothane pucks that some speaker stand manufacturers provide. Or, "Sticky" Fat Dots if you need to adhere the speakers. Placing Blu-Tak between a monitor speaker and stand does not couple the speaker to the stand, anyway (well, it sort of does, depending on what your definition of "coupling" is).
Rope caulk, available at hardware stores and cheap, can be used in this way, with much better sonic results than Blu-Tak. Rope caulk (Mortite is one brand name) is very sonically neutral and has many potential uses with any audio system.
Herbie's Audio Lab