I think weird things would happen if you allow both so I see the point but a shortcut like 2 or 3 clicks for DD might be nice for next gen.
Since it’s possible for DD to be the same as CC high due to battery and LED combo it could have 2 identical modes in a row if it worked that way i guess.
With all these current limited LEDs we are really missing out on these drivers. I hope you are able to get the store figured out before too long as it really feels like prime time for linear drivers. Who knows next year we may be flush with buckboost drivers and some obscure 9V LEDs or something.
Linear drivers will stay in flashlight world as long as source of light are LEDs, they are smaller, cheaper and have higher power density compared to switching drivers and that will not change. Also linear drivers can have wider dynamic range of currents without large penalty in efficiency,for ex. it's much less challenging to make linear driver with output adjustable from 0.1mA to 20Amps.
Another advantage is driver quiescent current while driver is active - it can be in xx uA range, which is almost impossible for switching drivers (mA range), so runtime on moonlight/very low modes can be significantly better with linear drivers.
While switching drivers in theory have higher efficiency, in practice (single cell - 3V LED) difference in average efficiency is 5-10% typically - not as high as many here claim. Reason for that is battery voltage drop, so linear drivers maybe start with ~75% efficiency when battery is full, but as battery voltage drops efficiency raises to ~100%, so average efficiency is somewhere in between, depending on which mode you use the most. If flashlight is mostly used in lowest and highest mode, there is almost no difference in efficiency because switching drivers efficiency is not that high either on those modes.
Switching drivers are only option when number of cells in series is not equal to number of LED "dies" in series.