I'm mulling this question over myself. My daughter knows about the bicarb and while I don't think it's necessary yet to use it, you can be sure that usage will spread like wildfire through high school runners. We've already seen kids in our area using lactate meters and doing obvious double threshold plans (easy to spot on Strava). Anybody who pays attention to competitive running is going to be facing this question.
Just like the supershoes, etc, if you don't use the bicarb, you'll eventually be at a disadvantage. These are kids competing for not just state meet spots and championships, but also scholarships. A few seconds could make the difference between taking huge student loans or having someone else pay for your school.
So my approach with my daughter has been to keep her informed, while encouraging her to improve without it and then we can evaluate later whether it's something she wants to consider if it's going to be a close call for state qualification or something like that. In her case, she's so far ahead of where she was last year, she's gonna destroy all her PRs significantly. I could only see her using it if it's going to be the factor that puts her over the edge in some important way.
What other posters have said about using it before the meet where you're going to need it is spot on. If my daughter ends up using it, I would first want to see her use it for 2 separate interval workouts, then in a throwaway dual meet, then in an invitational setting (but not the key race). That's what I'd recommend for anyone whose child is going to consider doing this.