My first experience with FreedomPop was I ordered a small Samsung headset to see if it was a truly free service. It is. Since I had their smartphone, voice service was over Sprint, which is decent in my area. Free 500mb of LTE data. If you don't use at least 1 kilobyte of data in a three-month period, your data gets suspended. So every now and then I was reminded I still have this service because of that.
Once they started offering GSM service I ordered more SIMs and followed all the recommended steps to downgrade to truly free service. I now have a total of 3 accounts. I keep one SIM that runs on AT&T in my iPad (for 200mb of free data). I linked a bunch of "freedom friends" go be gifted an additional 500mb of free data monthly. I use the other two accounts to "donate" 100mb of free data each to the AT&T SIM. So that gives me a total of 900mb of free data for the iPad. For the last few months, FreedomPop has consistently bumped that 900mb up to an exactly odd 1.07gb (1,031mb).
I've been using them since April 2013. Good for data, not so much for voice in my opinion. Unless you are getting the SIM for GSM devices, they use the Sprint network.
The biggest problem I've had is that by default, when usage gets within a certain amount of your limit, they charge your card and add a credit to your account in case you go over. The problem is these credits "expire" if they aren't touched for 90 days, meaning if you don't go in and click "renew" to re-apply them, you can accumulate quite a bit of unused credit.