Good Evening/Night/etc.,
Yeah, that's a whole lot for a very low price. If you've looked up the practitioner/s involved and all's legit, you can't beat it.
Some facts: The highest attenuation you'll get with custom earplugs is 25dB, and, like all attenuation figures, the above reflects average-attenuation across the measured spectrum, which appears to be up to around 8kHz, right about where the last pure-tone is tested for a traditional air-conductance audiogram (English: Like your typical hearing-test). Regardless of the name on the earplugs, the actual filter is made by or under the supervision of
Etymonics. Always. This I was told by one of the head honchos @ a top-5 hospital's audiology department.
Given that you're a drummer, I'd
HIGHLY recommend that you go with that 25dB filter for both ears, if you choose to go this route. Note that the only "custom" aspect to these earplugs is the earmold. The dB-filter is mass-produced and removeable. So, if, say, a person wants to use the 9dB filters for one application, the 15dBs for another, and the 25dBs for yet another, all s/he's got to do is fork out the money and purchase the filters. Some people use differently attenuating filters for each of their (usually) two ears, but I wouldn't recommend playing with aural fire b/c that's what that is.
There are, of course, earplugs that attenuate far more, but they are generic foam plugs you can get for near-nothing at your local drugstore. These ear-stuffers are without the relatively linear attenuation you get from the custom and other "hi-fi" plugs. They bring the incoming hi freq dBs w-a-y down, often beyond the 40s. That results in the
muffled sound that causes most musician users to rip those things out of their ears, which is totally understandable but defeats the purpose.
Caveat Emptor: Some drummers find that their kits generate so much noise that they go with over-the-ears protection, i.e., special "active" headphones that reduce ambient sound up to 33dB and plug into the board or such. Then, you can control how loud you want the incoming signal to be. If you go that route, you need to be very careful: Like in-the-ear monitors often seen in the ears of big-money players, you can end up cranking up those tiny in-ear monitors, thus listening to the music at levels above the actual volume of the entire band. That's not good. It sounds dumb, but we all know how high playing music can get us...so high that we "lose our senses," if you will. I know: I used to live there in my 20s. The loudness-induced trips were fun (high-volume is intoxicating for many), but the tinnitus

I'm lucky that I have no hearing-loss. Now, older, wiser, and sadder, permanently cured of YMIS, I always wear my ER-25 plugs when jamming or performing.
Good Luck.
Note: My comment should in no way be construed as a substitute for a face-to-face consult with a graduate-level (e.g., audiologist or ENT physician) hearing professional.