I did get the Telestial one, and for the most part it's been ok. The rate to make calls or send texts is a little high, but it is nice to have some of the features they include (like having a US and UK number on the same card). If you'll only be in 1-2 countries, it may be worth it to buy a SIM card from each country individually, but if you're going to be travelling all over it may be worth it to get the Telestial one so you can keep the same number.
I was also thinking of looking at phones that can take 2 SIM cards, that way I can have a local card for local calls relatively cheap, which would be great for me in Spain when I know some people, and that Telestial one for calls to/from home.
Edit: forgot the most important part. At first, I had trouble using it once I got to Spain. I could send text messages, but I couldn't make calls. What seemed to fix the problem was to switch it from automatically connecting to a random company's network (default was Movistar) and specifically tell it to connect to Vodafone's towers instead. Since it's a roaming card, it doesn't really matter which company I connect to, and I had good luck with Vodafone when I was in SVQ a couple years ago.
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