Very fine IEMs. I listened for a while to them as they were sent and liked them quite a lot, and then got around to dealing with the filters ("Nine Tail"). It is all very simple, and effective.
The filters (front & back) are color coded champagne, red and blue. It ships ready to go with the champagne filters. I really only listen to acoustic, so I used a recording of Mozart violin concertos on modern instruments with an historically informed interpretation (P Frank, D Zinman, TOZ). The filters sort themselves out immediately:
Champagne: V shaped.
Red: Strong impactful bass, relatively (slightly) muffled and distant. Everything in its place.
Blue: Flat and relatively airy. I immediately liked these.
A closer look at the 'back filters' sorts it out further as these are the vent ports and the 'front filters' are the actual filters. The vent ports go blue (fully open) champagne (partially open, 1/2, sounds open but not so airy), and red (pinhole open, sounds closed). So acoustic (blue) likes open and electronic (red) likes closed, and champagne for all-rounder. And the most likely combos are obvious: red filter with red or champagne vent ports, champagne filter with any vent port, and blue filter with blue or champagne vent ports. In case you were wondering.
Very coherent, likable and even sound. The blue filter is truly flat and nothing sticks out. The reviews that say the 9 Tail is weighted to the bass are in error, it is so only if you want it to be so.
lexs, Wb650 and ShakyJake are spot-on. A real nice listen, and great for acoustic. I don't know if Drop will be offering this again as it seems that myself and 4 or 5 other lucky people got it, but I certainly think it deserves another go.
HeadCaseyMDThanks a ton for the description of the filters. I got one recently and was a bit confused with the filters given there are virtually no instructions anywhere. I have the blue - champagne combo and they sound spectacular with a decent headphone amp