This is a combination of the previous HGBF Lightning Gundam and the HGBC Lightning Back Weapon System Mk-II.
I like the form equipped with the Lightning Back Weapon System because it's well-balanced, but the form with the open-barrel Hyper Beam Rifle and this rugged booster is the perfect form of the Lightning Gundam☝🏻. It's one of the coolest Build-type models (in my opinion😊).
In the anime, the scene where it follows and surpasses the Gundam Kyrios (flight form) which uses Trans-Am at high speeds with incredible maneuverability in mobile suit form is heartwarming.

HGBF 1/144 Lightning Gundam Full Burnern | ガンキチ's Gunpla works