I don't have much of an argument against the current module categories, but there DO seem to be some points where this could be improved.
For example, "Delay" contains EVERYTHING that delays a signal of some type somehow. So if you want an echo-type module, it's here...but then, so are trigger/gate delays, which aren't at all like the first example. You can kindasorta get past this by using the second category blank ("Clock modulator" finds the binary signal delays, "Effect" helps with the audio signal delays, and so on) but if the user who posted the module didn't add any of that to the "Category tags" on the module page, you'll miss it.
The "not-dual/not-quad" issue is another one. In some cases, posters for these sorts of modules that aren't either of those occasionally will put "triple" units into one or another...but it's far more normal for modules that fit that criteria to only be listed in their primary function category. For example, Zlob's VnIcursal VCA: six VCAs behind one panel...but if you're not looking for a "VCA + Mixer" in categories, you either might not notice it or, if looking in the "dual" or "quad" categories, you can miss it altogether!
Another annoyance: buffered mults vs. passives. Pull up "Multiples" with 2 hp chosen as a size limiter...and you get deluged, requiring you to pick through the results all the same. A "buffering" category could be an appropriate fix here, plus it can include devices other than buffered mults.
A few years back, I would've likely said this was all nitpicky. But given the explosion in the overall size of the databases here, some of these "basic" descriptors are running into problems as their categories are being stuffed chock-full of modules! "Oscillator", for instance, contains 1,235 entries in Eurorack alone. Sure, you can limit this further with a second category...but now, even THAT results in a plethora of entries; going to "Oscillator" and "Digital" still turns up 211 entries.
The worst part of this is that any fixes will require not only site recoding, but it'll ALSO require a knowledgeable crew to go through ALL module entries to add/remove flags as needed. And yes, without the manufacturer lock in place; this is another problem altogether, though, as manufacturers use the lock and then more or less abandon the entry pages, which helps no one. Frankly, if I had a dollar for every time I've had to point out that Clouds is a discontinued module, I probably coulda bought Mutable Instruments themselves, lock, stock 'n' barrel! So it's a potential nightmare if approached wrong...but if done right, it'll STILL be a huge undertaking, but it'll result in a fully-revised database.