I've had my Pono player for a few days now. It's doing everything I want it to, simply and easily, and the sound quality is excellent with my Denon AH-D7000 'phones connected directly. I have done brief comparisons with my Benchmark DAC1 HDR. Sometimes I think I hear a difference, other times not. One of these days I'll connect the Pono's line-level output to the analog input of the DAC1, play the same file on both systems, and find out what happens.
In the CD-quality vs. hi-res debate, I've come down on the side of CD quality. I've made live recordings at 24b/96k and compared those to downsampled versions. I've made 24b/96k LP transfers, and compared those to downsampled ones. Maybe I hear a difference, sometimes, but it hasn't been enough to persuade me to buy the "Studio Master" versions of downloads from Hyperion Records. The biggest effect on final sound quality that I have found comes from the original recording and mastering. I have some 1982 Denon CDs that sound as good as anything I've ever heard, no matter what the data rate is.
So, to me the Pono player is a definite win and an amazingly good deal at $400. The lack of features, such as pass-through DAC and EQ, doesn't bother me at all. I simply want a music player. I have had to make one accommodation with it, by adding album art to any album I want to play on it. On my main system (Mac Mini) I just use the Itunes text display, but managing the Pono is much easier with images.
There is one nitpick: The player makes two definite clicks through the headphones when it starts to play a new album. The rest of the time it is silent, and it plays back what's in the file.
Other devices I've used in this role:
Sony portable CD players and MDR-CD7 headphones (wore out, no replacements available)
Archos AV500 (would not play the Windows Lossless files I used at the time)
Squeezebox with Benchmark DAC1 (sounded good but was finicky and required a computer running)
Sound Devices 722 recorder (an experiment, as it's not designed for this role and won't play gaplessly but sounds very, very good)
Apple ipod touch (despite Apple's info, would not work with my main system, but worked fine with Windows 7)
Astell & Kern AK120 II (worked well enough, sounded good, had defective MicroSD card slot and required separate software on Mac)