I don't like the fusions too much myself but my dad uses them, why do they have the manual and the power cartridges if they are exactly the same but in color, "manual blue", "power orange". But is there a diffrence at all? Also are the old fusion cartridges compatible with the proglide handle and vice versa, in other words are all fusion cartridges compatible with all fusion handels. . manual, power, proglide manual, proglide power?