First, you need to understand how the juicedLink works. It defeats the AGC* by sending a loud noise or tone to one of the DSLR audio channels which suppresses the audio compressor. This means that only one of the two channels will have the sound of whatever you pointed the mic at.
When editing the audio you will have to split the stereo track into two mono tracks and mute or erase the noise/tone track. The signal into the DSRL will be hotter than if you used just a mic, so you will have a somewhat better Signal-to-Noise (S/N) ratio, but you are still running the audio through the DSLRs audio structure. In other words, you will have less hiss, but it will not be completely gone. Keep in mind that a DSLR is a still camera being co-opted into doing video work; the audio implementation is quite substandard.
The trend these says is to use a separate audio recorder. This is a case of two steps forward, one step back; a separate recorder has been used since talkies first arrived in the late 20's, and is still used with film to this day.
For less money than the juicedLink you can get a Tascam DR-100 (the MkII is due out this spring). For $600 you can get a Marantz PMD-661 or Fostex FR2-LE, which are true entry level production sound recorders. I've written many posts about all of these recorders and much more about production sound, so do a quick search here on IndieTalk. BTW, once you get one of these recorders you may want to get a low impedance XLR mic (NTG-1, AT-875, AT4053b, etc.). This will allow more flexibility and longer cable runs.
* AGC Stands for Automatic Gain Control; AGC automatically raises and lowers the incoming volume with a compressor that makes soft sounds louder, and loud sounds softer, so in quiet sections it even raises its own self noise (hiss)!