We used these years ago and as others have said they do appear at first to be good value.
We discovered that wasn't really the case.
But the biggest down-side for us was that for those times we really needed to get a line we found the access numbers either unavailable or busy.
There are plenty of good alternatives around. My wife has been using Lebara for a number of years now. May not be the cheapest all the time, but certainly the cheapest at many times and especially when they have a promo.
Besides which my wife has never had any issues with the network.
