My favourite situation in which I use Flea roll is of course wake-up In any combo like u/f+3+4,1+2,u/f (after u+3+4, Bad Breath, in okizeme on lying opponent...) I often don't finish it with f+3+4 slide to gain better positioning. My opponent mostly quickrolls in this case, so Sword Sweep is 90% likely to hit. Versus backdashers I use FC,d/f+3 (if they try to backdash out of range). And if I predict they want to attack immediately, u/f+3 is best.
Flea roll is very useful. I usually connect the follow-ups. The key is to keep a pressure. Opponent standing up is much pressured by this movement. Especially in my style, in which I base my strategy on okizeme.
Believe me or not... but many of my sparring partners get seriously irritated on my style. Sometimes I have never seen them being so mad... So while reading my FAQ, be awared that you can be kicked and punched in real life for the tricks you'll learn, I warn you.