I have an Iridium Extreme. It's a superb piece of kit. One of my most valuable pieces of kit.
If you're going to purchase one, don't look at other brands as they don't have as good coverage as the Iridium. I've used mine on trips to the following and its performed flawlessly:
Limpopo Province, South Africa
Northern Territory, Australia
Kariba, Zimbabwe
Colorado, USA
Rede, Hungary
I bought mine at the beginning of 2012 while I was preparing for a very remote trip to hunt water buffalo in Northern Territory, Australia. My main purpose for getting it was the remoteness of this particular trip, incase we needed to get a fly-in doctor or something, and also in case my staff needed to get me as I run my own business and left them at a critical time in a project.
I also looked at renting one, but made the decision to buy as it meant that I had one handy for other trips.
I have no regrets buying mine and take it on every trip I go on, even if I get "normal cell reception", it's nice to have it "just in case".
Also, I've had great dealings with the UK authorised dealer of Iridium and with Iridium HQ in the US, so can vouch for their customer service.
Hope this helps. Please shout if you have any more questions.