In short: Direction does not impact it, these are just new animations and it is just a boost when you land still.
As seen here (and my own experience with Mario Kart games that implemented this):
"A Trick (also called Stunt) is a technical move that first appeared
in Mario Kart Wii. After jumping off of most ramps, characters can
perform tricks. Upon landing, the player will get a Jump Boost. If
launching off of boost panels, karts flip horizontally (similar to a
corkscrew motion) while bikes flip vertically if using the Up or Down
controls. Tricks can also be executed on boost panels itself."
There is some more detailed information there about combos, trick types and the history of it.
"Tricks are known as Jump Boosts in the stats screen (in version
2.0 and later) and the e-manual. In certain courses, it is possible to perform Trick Combos, which consist of multiple consecutive
tricks to gain a much longer and faster boost."
To clarify as per my understanding about the above quote - performing consecutive tricks (jump boosts) in a row will increase your boost and extend it. Repeatedly performing tricks off jumps in quick succession, not multiple tricks in the air.
"Stunt Boosts return from Mario Kart Wii. When you're heading over any
major ramp or small bump you press the R button. If you time this
right your character will perform a stunt and get a boost forward, but
if you time it incorrectly you'll just do a jump and lose speed as you
fumble up and over the ramp."
This source showcases a lot of different jump animations, which further solidify the idea that these are just for showboating and fun.
And finally there is another wiki that states:
"In Mario Kart 8, when you using the Wii U GamePad, you are able to
control your tricks. For example, if you were to tilt the control
stick up, the character would do a forward flip, but if you were to
take the control stick left, the kart would spin left. Also, the sound
made when performing tricks has changed."