I'm very pleased with mine, it only took 2 days to come, very good service there. I bought it primarily for use with my laptop, using USB (sadly no optical on my cheap laptop) the output from the Fubar IV is night and day compared to the headphone socket on the laptop.
I'm not very good at describing what I hear, but I'll have a go. The sound is clean and crisp with a good dynamic range, detail resolution is great, it'll drag out instruments I couldn't previously hear. The sound has greater width (is that the right term?) than before, bass isn't overblown, mind you my old Beyer DT331s are fairly light weight, but I like the result, although new headphones are at the top of my upgrade list (and as Chebby said - then the Supplier, then a new op-amp...).
All in all it's a very enjoyable sound, I even listened to 2 albums on Spotify last night, I could have listened longer but it was getting late.
I bought the Fubar IV in isolation so I can't comment how it compares to other DAC/headphone amps. At 125EUR it was a bargain, even at 225EUR I think it's still a bargain. And it is sooo cute
p.s. If I can find my one and only optical cable I'll plumb my Humax 9300T into it to see if it can improve the DVB radio.