How are you giving anything away? If they refuse to block low, why the hell not D4? 212 is still guaranteed for the most part and then you just added 3% damage to it. That shit adds up, and the strategy could be nothing more then that. Stacking damage. You're not at all saying "HEY I HAVE F4".
Which is all, of course, based on opponent reads, meter/HP ratio and character, but I didn't mention anything about that. Would I waste the advantage on say Kabal or Raiden? Fuck no. Would I go for it on a character with shitty pokes, slow normals and lack of armor? Hell yeah.