I have used these in a couple of rooms, you can run up to 150ft:
They work great with a few caveats:
1) For whatever reason, I could not get them to work with cat6 cables I had crimped myself. I guess they just didn't make a tight enough connection. I bought some cat6 wires to go with them and they worked just fine.
2) These do not pass power, so if you have a device that needs power from the HDMI (like maybe a signal booster), its not going to work.
3) While it worked flawlessly when I had my HTPC outputting the video directly to my projector, when I bought an Onkyo 709 and started feeding the HDMI to it first, then the projector, I got bad signal breakups. Seems that the strength of the signal going out of the Onkyo is kind of weak (lots of complaints about that online). Not sure about other AVR's though.
All that said, if you ar using WMC as your DVR, this may or may not work. You said it was for OTA broadcasts, so this might not be an issue, but when I tried to output video onto two displays (using cablecard), I got DHCP errors left and right. Also, if you are using a splitter, realize that the best audio you are going to get is what ever the lowest level is of your three displays. (IE if you have an awesome AVR with 9.1 surround sound in one room and a small TV that only handles Dolby 2.1 in the other, everything is going to get Dolby 2.1).
If you are just using this as a DVR, the extenders are largely flawless. I have an XBox 360 in one room that I use only for viewing live and recordedTV. Picked it up on eBay for $99. Been using it for years and never had a single problem. I don't have an Echo, but it seems like most of the problems with it have been around trying to play content like MKVs, not with live/recorded TV.