I have been using it for over 6 months now to talk to family back in the states. I have read about the adware/spyware, but I have not had any issues. I am not saying other people didn't, but it is fine on my wife's laptop.
As for the functionality, I can't beat it for $20 a year. ($40 for first year includes product). You do have to have the MagicJack plugged it to make or receive calls, but you can use a headset, or plug your phone into the jack. When traveling I just use my headset and the software on the jack, here in Germany I have my phone plugged into the jack just like it was a standard wall jack, but I don't leave it on all the time.
Another good function is I have it set to send an e-mail (with audio file) to me when I get a voicemail. This allows my family in the states to call it and leave voicemail, I get it on my iPhone and call them back. Not too bad in my opinion, easy to use and makes the family happy they have a way to reach us sometimes.