So I'm very convinced that Burning Spin Dash is Sonic's best Side-B by a long shot and the guide doesn't even begin to explain the real pros about this move (or any of the custom moves but that's w/e).
The lack of jump height mid-attack is actually a blessing in disguise. When Sonic jumps, he does so at short-hop height (while still keeping his Spin Dash hitbox) as opposed to the Spin Dash 1's full-hop height. It's bad for follow-ups but makes Spin Dash incredibly safe on shield when as once Sonic touches the ground again, he's in neutral stance where he can preform any action. What that means is that, unless you're fighting Sonic or Little Mac, the hop still travels faster than characters can drop shield and chase you so jumping when you make contact with Burning Spin Dash is safe regardless of whether or not they shielded.
The lack of a hop on start-up is made moot by the fact that Burning Spin Dash beats, destroys, and continues through weak, non-transcendent projectiles. These include things like Mega Man's Metal Blade and Crash Bombs, ROB's Gyro, Greninja's uncharged Water Shuriken, and Wario's Bike when riding it. No need for the move to have an invincible, telegraphed start-up hop when you can just eat projectiles like Wario. Speaking of Wario, Burning Spin Dash's fire hitbox reaches further than Wario's Chomp and beats Bike so that MU is probably in Sonic's favor this time around.
It also does a solid 30% at low percents with the combo of SD > Hop Hitbox > Sweet Spot N-Air.
Not using Burning Spin Dash is silly. Sillier than not using Double Spring (aka invincibility on demand) or Surprise Attack (the most threatening off-stage move in the game.)
With customs being legal in my region, I'm gonna have to main Sonic again. Custom moves make Sonic a high-tier threat, not quite Sheik or Greninja levels but goddamn are we up there.
Well, I'm not going to use any custom moves at all, so if you've been using them and actually know some GOOD uses for them, just post them here and I'll put them on the guide.
BTW, sacrificing combo-ability up to the higher percents with TWO specials (rendering one of them practically useless in the process) in order to be safer on shield and eating through projectiles that can be circumvented in another way is not what I'd define as "best by a long shot", but w/e.
EDIT: oh, unless if you use SD3 and HA3, then maybe it's a thing, since HA3 will be useless on the stage and you can use SD3 to avoid projectiles instead.
And if you do use Double Spring and actually get something positive out of it, please do tell. I'm genuinely curious about that.
EDIT2: wow, just wow. I tried using Burning SD against a CPU and the first thing I noticed is how the move goes to a DEAD STOP when it hits a shield. That's just gross.
EDIT3: tried jumping before hitting the opponent. Forgot that this move acts like a SDR from an aerial spin. SD (not the move) ensues.
EDIT4: after messing around with SD3 for a bit, it does seem promising (spam: SD3->SDJ before reaching opponent->Uair->repeat), against CPUs, at least. They don't react well against the move and won't counterattack most of the time.
Against a competent human, I doubt it would bear much fruit in the long run. A well-timed spotdodge and a Smash attack should break this chain of spam easily enough. Or, even better, a backwards roll would put them right in front of a Sonic landing right after an aerial.
So, yeah, maybe I'm not understanding how you said the move should be used but I'm still not buying that this custom move is the "best by a long shot".