On balance, I'm hoping. Because...
One day, when yet another "Terraclean/BG244/BG44K/whatever" thread gets started (by someone who hasn't bothered to search the forum first!) there'll eventually be a proper reply from someone knowledgeable (but unbiased!) explaining exactly how it works, what the realistic benefits might be (worst case as well as best case!), what scientific/engineering trials have been performed (with results), how long might the benefit last, exactly what is getting cleaned (i.e., the fuel side and/or the engine internals), where does all this removed crap go without causing damage to the catcons, etc, etc.
Anecdotal evidence from previous customers/users is all very well, but unfortunately these are quite likely to exaggerate (or imagine) the claimed benefits thanks to the (surprisingly powerful) placebo effect.
Some benefits ARE real, but very temporary (e.g. BG244/BG44k) where the stuff is loaded with cetane/octane boosters, which may well give a noticeable performance benefit, but only while the stuff is still in the tank!
And I really don't care if Edd China (who gets his 'stunt double' Paul Brackley to do all the mechanical stuff anyway, once the TV cameras go off him!) swears by Terraclean.