I've been practicing doing the hopping trick in Royal Raceway and I can see the benefits. The trick seems to be eliminating non-linearity when cornering, basically you slow down when alternating between drifts because the kart has to physically turn, while it also seems to provide better speed if you leave the ground I assume. So you can use it to bridge the gap between multiple turns without having to readjust the direction you're facing. It also improves large boosts and works for about 4/5 consecutive hops, this seems to work with a long drifting boost the same way. The cornering allows you to run a very narrow racing line because you don't have to account for your kart steering off the track as much when close to the edge. It seems easier to do with the d-pad.
So is it reliable? On simple corners it's very easy to do consistently and get a slight incremental benefit, or on the long boosts it's a given that doing 3 hops will be safe for the benefits, but doing it on every single occasion with maximum efficiency like the time trial does seems extremely risky because of how close you're running to the edge of the track which can cost you dearly with a single mistake.