I have had two refurbs, the first was a HR20-100, which lasted 4 months, then I started having constant reboots. They sent me a replacement, which is a refurb HR20-700. I've had it for three weeks, and it so far has been fine. I know that you can't request a certain model, you get what you get, and most of the time when they are replacing or upgrading you for free and shipping it to you, you will get a refurb.
Sometimes you can get lucky if you have an installer come out, they will sometimes have new units on the truck, and sometimes have a variety of models. I had a guy come out in February who was going to give me my choice of a new HR20 or HR21, and he also had refurbs on the truck. Unfortunately it was too icy on my roof that day and he was there to install the 5 LNB dish. He couldn't do the install, and couldn't/wouldn't leave the box with me for the next installer. When the next guy came a day later, he only had HR20 refurbs on his truck, so that is what I got.