I have my sitting behind a USG Pro and its working flawlessly.
Note at the moment it is direct streaming so no need to set up IGMP etc - downside is that it is therefore using part of your capacity but average bit rate looks to be around 8-10 m/bs so about 10% of my 100mb/s and I don't notice it.
I have heard that they might turn some multicasting on down the track, in which case IGMP would be required. Which I have never had much sucess on for the old VTV boxes so if that day comes I might have to resort to what I use to do and run two networks - one on the USG and another on the Vodafone modem. The edgerouter may be easier to set-up IGMP.