Here's a link to a series of tests of various audio devices and the Canon 5D MkII, this is the conclusion but you'll find links to the other tests on vimeo.
Even though they used the 5D it should hold true for the 7D. And they test standalone recorders like the H4 so you can hear the difference between those and the Beachtek direct to the 5D.
-a-
Just watched the video posted above... The JuicedLink looks great but it doesn't seem like it would work without that custom firmware. And it's not yet available for the 7D. http://magiclantern.wikia.com/wiki/Magic_Lantern_Firmware_Wiki .. Unless I missed something?
I run the juicedlink into a Sony PCM-D50 and have headphones connected to the D50 for monitoring and then running line out to the camera which becomes a dual recording system.
I've shot stuff yesterday with the JuicedLink CX211 on the 7D. Works as expected, but the big problem is lack of monitoring.
You need to unscrew the plastic locating pin on the JL to be able to screw it under the 7D.
The little 1/8" cable could be a bit longer (or maybe a "twisty" strechable cable) to afford more flexibility in mounting orientations. I mounted the JL "sideways" with the XLR inputs facing towards the back.
From using the product on my HV20 (which does have an headphone output, manual levels and VU meters on camera... sigh...), I can vouch that JuicedLinks are a great value.
H4N is much better choice because of pre-amps and it recording power. Plus, it's 96 Khz 24 bit with great limiters - not available in even a juicedlink box.
Beachtek is not my fav solution, even for camcorders. Juicelink if don't want double-system or H4N.
The Beachtek 5D works fine...not great..just fine. I used it in my latest short. If you listen to the audio, it all came directly from the Beachtek box.
I just dont think that the issue is the Beachtek or any box...it is the camera itself. The camera will create interferance noise if you connect HDMI out to a monitor, or connect the 7d to the AC connector..then your whole audio...no matter what you are using will suck.