Sekku is +2 on hit and cl.lk / cl.mp both have 3f of startup. You need a counter hit to link it. Since sekku is a medium kick, on CH it gives additional +2. 1 frame link, plink cl.mp and it will work.
But like Lion_Jak said, you need the opponant to hit a button and you also need to do the sekku in their face or you will be too far to followup. And far lk / far mp aren’t 3 frames.
So I’m afraid Ramma is right, I was messing yesterday with crouching Abel in training and it wasn’t possible to get a close lk/mp after the sekku.
iamPowPow, that video was deleted, because you have to meaty on the last active frame of the sekku. And the timing changes depending on crouching/standing plus it’s character specific.
You have more chance to frametrap after a sekku on HIT, but you will have to condition the opponant to press a button. But the -2 on block and the fact to be in their face, can’t press something