A few months ago, I purchased the beachtek 5d unit. While it worked wonders for the first two months, the unit completely conked out while on a commercial shoot in Miami. This is totally unacceptable and after talking to fellow filmmakers, they had similiar experiences. I decided to go for a dual system sound option.
After testing both the Tascam DR-100 and the Zoom h4n (the go to model for 5d mark II), I decided to go for the Tascam. Here's why. The first difference were the on-board mikes. TASCAM is a pro-level brand and the sound quality was shockingly much better than the H4n. 
Secondly, the TASCAM has both a headphone out with dial controls and a line out, which means that you can send a signal to your camera while simultaneously monitoring the Tascam. Because of the headphone dial you can use it like a built in attenuator and if you set the headphone dial to roughly 3, the signal is clean into the camera eliminating the need to sync sound later in post. This is a huge advantage over the H4n which only has one output. 
Furthermore, the unit has separate volume controls for the XLR inputs another short coming from the H4N.The build quality is excellent with most of the controls you need to use easily accessible with switches. The body is all metal. The pre-amps on the XLR inputs are excellent. It has two batteries a rechargeable lithium battery as well as AA batteries. Like the H4n, you can easily mount the unit on your camera with a hot shoe adapter. My tests allowed for about 7 hours recording time with the two batteries.
I bought the unit for $329 at Dale audio but i did notice that the price has gone up since my last purchase. You can still buy the unit for about $310 on Amazon.
CONCLUSION: HIGHLY RECOMMENDED. The TASCAM out preforms the H4N in every category except for one and that is the option of 4 channel recording from the H4N. But since I was so disappointed in the on-board h4n mikes, I concluded i would probably never use it. It is the ideal system for external sound for the 5d.
