It is useful, the mix up potential give you a lot more damage. For example, if you manage a GF throw, it is 300 damage in total. Plus it is an untechable knock down afterward.
If you just do a HK tatsu, it is just 185 damage, and they are all the way across the screen. Good for people you can zone easily like E honda, Thawk, etc. Bad for people who can just wait it out and out lame you like anyone with double Fireballs.
As for Execution problem. The problem is that depends on hitbox of your opponent, the timing is slightly different. You are going to need to practice the j.mp after backthrow against several characters. E.Honda, Hakkan, Blanka, have completely different timing compare to Ryu / Ken. And those also have completely different timing with Cammy, Makato and Ibuki from my finding.
Maybe someone need to complies a list of timing for this… but since the wait is rather lengthy, it might be hard to gasp.