Disclaimer: I am not an audiophile.
I bought the ART DJ Pre II for a relatively specific reason - both my record player and my AppleTV (via a bluetooth receiver) were outputting directly to my living room speakers, and the record player signal was MUCH quieter than the AppleTV, even with the AppleTV turned all the way down.
Because of this, each time that I wanted to play a record I would have to go over and manually turn UP the volume. And afterwards, you would have to remember to turn it back down - otherwise the AppleTV would be ear-shatteringly loud! Quite an annoying situation.
The ART DJ Pre II provided a very flexible and clear way of boosting the phono signal to match the volume of the AppleTV. Unlike many other phono preamps, this one has an easy gain knob that lets you dial in a specific amount of amplification.
Because of this, it was incredibly easy to manually adjust it so the two signal strengths roughly matched.
No more shockingly loud movies from the AppleTV! No more putting on a record and straining to hear anything. Finally everything was in balance.
So in summary, the plus points:
1. Easy to setup
2. Easy to use (volume adjustment is very nice)
3. Sounds like a clean preamp, not coloring the sound in a detectable way
4. Inexpensive
All in all, I would heartily recommend this preamp - the volume knob alone makes it worth buying.