I have one and have had it for well over a year.
I've had some issues with it, other times it's worked great. You MUST have your computer on at all times if you expect to receive calls with it.
I only use it when I travel over seas to call back to the US.
They say you can replace your home phone. As Hertz says, "Not Exactly".
Even if you do travel with it, you have to have an actual phone to plug into it. I suggest just using Skype with a subscription that allows you to call cell/land lines and getting a headset.
Less stuff to carry with you. You can even buy a Skype phone that doesn't require your computer. You just plug it into your home router.
I give it 3 stars. Three because you can call land lines and it's only $20 a year. Skype is a bit more than that to call land lines for an entire year I believe. Not much more though. Skype is the better option.