Get a pair.
The FA-003 is a really good headphone for it's price tag. So something less expensive that is just as good is down right amazing. The FA-003 reminds me a lot of my mid-tier headphones. The range is excellent. The FA-003 definitely is unforgiving though, it has a small treble spike some where in the upper region that helps pick out details and give an energy to the headphone, but it's not enough to become sibilant. It really reminds me of the treble and mids of the Shure SRH940, but, with a much bigger lower end that can hit 30hz without a problem (though it rounds off fast after that, but hey, all headphones do). The FA-003 does not need an amplifier, but this headphone scales actually. This is something that I definitely had to change my mind on; as I didn't think it really needed an amp until I started to extensively test it's bass capability. Amplification changes this headphone's ability to have a controlled low end in the sub-bass area. So my sine wave tests of 100hz to 10hz sound pretty different when I put them on weaker amps and then stronger amps (in terms of it's power output for the resistance rating). The sub bass fills out and definitely gets tight and controlled with good amplification. The headphone does indeed remind me of my Sennheiser HD580's (HD600's) but with a small spike in treble. The sound stage of the FA-003 is actually great, the cups are deep, and separation and imaging is great. The isolation is excellent. I don't have it measured, but based on other headphones I've tested, I would say it's easily 18~20db isolation. The impact of the FA-003 is the big difference between it and an open-headphone. This is very pleasing to me. I like closed headphones because of the energy and impact they can have, that open headphones cannot generate. The FA-003's can reach deep into sub bass and give you a good punch, kind of like a Denon can, and this is something that you feel which really aids in bass reproduction enjoyment in my book. On a lesser amp, the FA-003 didn't have the sub bass drop at 0:55 that I wanted in some dub. I plug her into something with more juice, and boom, that drop hits with impact and pretty good authority for a neutral headphone. So amplification on the FA-003 scales the headphone. And this was at moderate volume, to ensure it's not just a volume kick. At low volumes even, you can hear a significant difference in sub bass reproduction and control. I didn't notice any of this sort of magic in the mids & treble change with amplification that I can truly pinpoint. But again, it's not sibilant, yet very detailed, all the mids & treble are right there on your plate, not being washed away or being hidden at all. Build quality is solid, it's not flimsy and floppy. The plastic feels good and hard. The padding is generous. Cabling is completely detachable and long.
Anyone who wants a good headphone for every application, from casual listening to content creation, should entertain the idea of the FA-003 (or a rebrand). It's price does not reflect it's ability at all. But all of Fischer Audio seems to be underpriced to me, or other brands are just over priced.
It doesn't quite best my D5000 for my attention in terms of bass, but that's because I'm a sub-bass whore, so the D5000 always gets me there. But if you want something neutral, inexpensive, comfortable, isolating, with detailed good accurate reproduction with a good sound stage, the FA-003 is a very strong contender. I'm pretty sure if more people had access to this headphone, you'd see a lot less recommendations for things like the SRH840, M50, DT770PRO, HFI580, etc, except for pure bassheads, and the like, as this is in the same price range and doesn't get a lot of thread-time. But it should. But it's definitely true, it takes a while to get a pair since retailers are limited and shipping takes a long time. But it's worth the wait.
(Note, the FA-003 has more impact and sub-bass presence than the supposedly bassy FA-011, which I also have, frankly, the FA-003 has a bigger sound stage and better bass than the FA-011)