Currently there's no real reason to use flame fist at all. The variation doesn't have the pressure you're talking about or any rushdown potential.
The buff serves it's purpose well enough, and is easy enough to activate after a combo ender, or the ex off f213, but what hurts is how many tools the variation loses. Windmill fist is straight inferior to bicycle kicks: it's isn't + enough to set up any frame traps on hit, its fully punishable on block, and you can't burn meter in the middle of it to make it safe either. You also lose the ability to cancel fly kick into bicycle. With those, and fireball cancels gone, you lose any way to setup pressure on block since all of his specials are unsafe.
As a result, this variation is strictly used for zoning- so you have to get as much mileage out of the fireball and parry as you can. That said, you'll still struggle to find opportunites to activate the buff, most of the time it'll take meter, and the only advantage the low fireball has is that he stays crouched slightly longer. The chip from the buff is also negligable simply because he has no blockstrings long enough to take advantage of it.
Strongly recommend Dragonfire. I don't see many similarities to Kung Lao though, so the transition will probably be awkward either way. Liu relies primarily on his walkspeed- using it to fireball zone and trip guard, then alternating into his pressure with fireball cancels, forcing his opponent to choose between blocking or reading a throw. Lao relies much more heavily on his range, reversals, and frame traps.
