Pros: build quality, sound quality, many inputs, many outputs, fantastic company support, great looking
Cons: some might find it... plain?
If you have waded across the web all the way to this review, I'll assume you've already read some of the big forum threads on this site, and I'm sure you've already read all of the reviews on other websites and publications about this piece of gear, so you already come into this with some background knowledge about this device and devices like (or unlike) it.
I have the Benchmark DAC1 USB: the second model slightly upgraded from the original design of the now classic Benchmark DAC1. Before this, I had (and still have) a Nuforce Icon HD. I use both of these as both DAC and headphone amplifier for my Denon AH-D5000, and preamp for my KRK studio monitors.
I'll try to be brief and avoid much colorful, interpretive flights of language that you see all the time in audiophile reviews.
Sound quality: noticeably better than the Nuforce Icon HD. Volume balance between channels is perfect at all levels. Noise floor is noticeably quieter. Bass is a little quicker and more "real." Things seem just a little more clear in the mids and highs are nicer and less fatiguing/stressful at higher volumes. The Icon HD sounds fantastic to everyone who listens to it, and this I would say is a tier above that. Difference is not life and death unless you are exceptionally picky, but there is a difference and it is very good. There is no coloration to this sound - it is just accurate, clear and strong. Use an EQ with this if you want coloration, or look elsewhere for technically same/worse performing devices that come colored off the shelf.
Features, inputs, outputs: I can use this with pretty much any device that puts out a digital audio signal, and I can plug into this pretty much anything that accepts an analog signal. I can toggle between inputs with a really cool little switch, and one of the two headphone outputs is capable of muting all rear outputs when it is occupied. A switch on the back can change the XLR and RCA outputs from volume controlled (with the very nice volume knob) to flat, constant line level. Attenuators (-0,-10,-20,-30) for the rear outputs can be adjusted as well. There is no power button, it just turns on and off very effectively depending on whether or not you're using it. This sounds strange and untrustworthy, but no - it works great in practice. There is no display, but it doesn't need one. "It just works." Feed it a signal and give it something to output to, and that's genuinely all you need to worry about, marvelously simple design.
Build quality: this thing is heavy, sturdy, good looking, and sensible. It is large enough to be impressive but not so large that it is inconvenient. It does not feel like it will break, ever. Gets warm to the touch after use. Friends agree that it looks "awesome."
This is an exceptionally clear, high-performing and versatile device in a well-made package. If you want a good DAC/amp to control your powered speakers, and/or a good DAC/amp to power your headphones, this is the device of devices. It is simple, it works - and it works really, really well.
From the charts I've seen, you really don't get gear much better than this. You can get devices that color things differently or look physically different, but this is pure neutral pro audio right here and it is as good as any piece of audio gear needs to be. Everything competing against this or existing at a higher bracket than this is, in my opinion: either about prestige or niche coloration. You can get a device that rolls off the highs or uses unique sounding parts to make an exotic but nice sound that is somewhere east or west of "accurate" if you want - or you can get 100% pure sound right here with the Benchmark DAC1. Once you get to this level, things are strictly about personal preference, because price/performance becomes meaningless when performance plateaus and money isn't an object anyway.