How good is this ATSC modulator?

I've never before seen an 8VSB ATSC modulator that cost under $1000, until today. I found this here http://www.mcmelectronics.com/product/STELLAR-LABS-33-11980-/33-11980 which costs only $299. It appears to allow independent setting of the digital channel number and the physical channel (transmit frequency). It looks like a good deal, but I'm not sure. Before I spend that much money, I'm going to want to get some input from others who used it.
Here are some things that I'd like to know, and hopefully the community here will be able to provide some definitive answers.
Does it work with sound, or only video? (One review on Amazon, where it's also being sold, said they don't get sound out of their TV when using it)
Does it allow setting of the sub-channel number? (I can't find any documentation on this, so is it limited to using only the first sub-channel for each channel?)
Does it work with 1080p video? (one review on Amazon said it was downscaling their video from 1080p to 720p)

I don't know if the complaints on the Amazon reviews were just from people with defective units, or if these are actual problems with the device, so I hope some users here on this forum will have used this device, and will be able to provide some definitive answers.