Do you have cinder block? You can get great anchorage to attach these to the wall with that. They'll work fine if you have them installed properly.
Anything else - and I mean ANYTHING else, it's a no-go.
Brick is not durable, brittle, and you have to find the "hollow" spot in a brick (if using the standard ACME bricks in Texas) to drill into to anchor it, or you'll just have a bunch of holes of hope holding the thing up. My school put up art display boards drilled into brick. They stayed up for literally five weeks before they fell out of the wall.
If you have board walls, you WILL eventually have them fall out of the wall - or you'll put a hole in the wall when it pulls out. If you have 1/2" or thicker plywood to anchor them to, and you use REAL anchors and not just the plastic ones, it CAN work, but you're talking time and energy to install it properly. Unfortunately, if your school was built in the past ~50 years, you don't have 1/2" thick plywood. 1/4" to 3/8" is the "industrial" standard and has been for decades.
If you have drywall, don't even bother. Drywall can be WALKED through if you have any sort of determined effort. Hold up a $7500-8500 Sousaphone? No thanks.
Plaster is usually applied over brick or concrete walls, but may work depending upon your installation.
To be honest, there's a reason they're using a 3/4 size tuba and a fiberglass sousa to demonstrate them. The BRACKETS work fine as intended - the WALLS aren't up for the task. The mounts and walls can't bear the weight.
Plus, if you install them, you're basically designating a section of your band hall as "Tuba Land" since that's where ALL of them will keep ALL of their stuff ALL of the time.
And finally - does your school ever put any non-Band classes in the band hall, say, for testing purposes? Are they always 100% perfectly supervised? If not, hope you have bell covers! Otherwise, jerk kids will see the open bell hole as a basketball-related challenge.