F3/F4 mix is all about conditioning your opponent. F3 and F4 look pretty similar, so your opponent has to guess which one is it. I don't believe that its a risk because your opponent has to know that you are going for the F4 and if you don't they get hit and it starts all over again. As far as jailing goes, my go to is B3 since you get an extra 5 frames to press a button and it's a low and it has 10F start-up, also to 2 blockstrings (B3U4/B3D4).
Kill Frames
112/ 2 forward dash and S1 or S2 (if they go for an Getup attack U2 it will beat it)
112/ Walk forward slightly and then back dash F242 (Makes Getup Attack U3 whiff)
F3/ 2 forward dash and S1 or S2 (if they go for an Getup attack U2 it will beat it)
F3/ Walk forward slightly and then back dash F242 (Makes Getup Attack U3 whiff)
Also, S4 would probably be your best punisher if you are punishing a move that is 11 frames are higher.
B1D2 (High, Overhead) KB
B3U4/B3D4 (Low, Overhead/ Low, Low)
S3U2D2 (High, Low, Low)
F242/F243 (Mid, Low, Mid) KB
21U2D2 (High, Mid, Mid, Overhead)
F3 ( Overhead)
B2112 (Mid, Overhead, High)