It really depends on what you're trying to send the director. IF all he wants is the boom, then mono is fine. Even if he needs a mix of the boom and lavs, mono is fine. The problem you'll have is you just don't have much control on what you can send him.
For about 80% of what I do, I'm running only boom, and I record on both tracks of my tascam dr-100 in mono just so I can hear it in both my ears. If I've got something really dynamic with both whispers and screams, I'll split the boom, send each side of the split to the inputs, set one channel for high gain to capture the tender stuff, and set the other side turned down to catch the screams without clipping. I wear in-ears and hear each channel in each ear. For the other 20%, where I'm running one or more channel of lavs, I run the boom into one channel, and the mix from the lavs into the other, and then I'm hearing the boom in my left ear, and the lav mix in my right ear. This works for me but might drive the director crazy. I could also route the boom to the mixer if I've got enough channels free, pan the boom channel left, the lav channels right, and send the two outputs to the two inputs on the tascam.
Fortunately, the only time I've had the director ask for an audio feed is when he is operating the camera, or standing near it. In this case, I send the camera a line out from my tascam, plug in as line-level, and the director plugs my extra headphones into the camera. Notice even in this case I'm wired to the camera.
Bottom line, location wireless can really drive the budget thru the roof.
The unit you referenced looks like it only accepts a mic level input.
If you really have to do it, and don't a have a large budget, try
this. I use one at home for TV, and you can rig the transmitter to work with a 9v battery. Works on the same principle as the one you referenced, takes line level in, is stereo. Downside is the transmitter is not exactly form factor for location work, and you'll have to rig a battery pack to power the transmitter. The headphones run on two AAAs and a set of 4 will probably get you thru a whole day of shooting.
It's not what I would monitor my location sound with, but if you don't have much money, and the director is insisting on a wireless feed (but isn't willing to pay for it), it will give him/her something to listen to.
Some search results on
ebay and
Google.
I would have buy
this, but it is mono.