I think then that safeJG is a misnomer. It should be something like safe-failedJG. As I said in another thread, you're basically cheating yourself out of JGs.
Let me see if I can settle this Safe-JG issue once and for all. Say we have 3 players:
Player A always attempts JG with a single tap of G lasting two frames.
Player B has perfected the rhythm of the "Safe-JG" double tap. Every time he attempts a JG, he presses G for two frames, releases for exactly 6 frames, then presses and holds G again.
Player C also uses a "Safe-JG" double tap, but his rhythm is not as good. He always hits the initial G for two frames, but then releases for between 4-6 frames before pressing and holding the second G. For ease of comparison, we'll just assume the average of 5 release frames between his first and second tap for the rest of this example.
Now, using your example of Natsu's i10 A attack, let's take a look at the all the possible timings to attempt a JG.
If all three players start their JG attempt on F1 or earlier we get the following results:
Player A - Hit
Player B - Block
Player C - Block
If all three players start their JG attempt on F2 we get:
Player A - JG
Player B - Block
Player C - Block
If all three players start their JG attempt on F3 we get:
Player A - JG
Player B - JG
Player C - Block
If all three players start their JG attempt on F4 through F7 we get:
Player A - JG
Player B - JG
Player C - JG
If all three players start their JG attempt on F8 or F9 we get:
Player A - Block
Player B - Block
Player C - Block
Any later than F9, and any of our players are getting hit.
noodalls, can you now see how Player B's Safe-JG double tap succeeds almost as often as Player A's single tap?
Can you also agree that while Player C may get JG's a bit less often than Player A, its reasonable that he may consider that a worthwhile trade-off for the extra safety in case he initiates his JG too soon?
Safe-JG is all about rhythm. With perfect rhythm, it makes a minimal sacrifice in the JG window length to guaranty that the user does not eat the attack if timing is too early. With less than perfect rhythm, its a trade-off, but it certainly doesn't completely ruin your chances of getting a JG.