I've studied mate intensively (actually started my tea life by drinking mate at a camp with a bunch of argentinians which led me to green, white, and rooibos) and no one is quite sure if mate contains caffeine or mateine, a similar compound without the bad side effects (jitters, etc.). I do know that once you have tried mate prepared the correct way (it is very difficult to make perfectly), that you will enjoy the flavor. If it is still to much for you, then you can always add some stuff to it.
Adagio, if you are still looking for a good brand of mate, ask aviva (www.yerba-mate.com
) for some samples. They harvest some of the best mate around and they also have very good flavored mate. Also anyone that is interested, I highly recommend aviva.
There are also some other good brands out there. Cruz de Malta is one of my favorites. They offer some good flavored types (lemon, lime, orange). Rosamonte is also a very good brand (very strong though). www.gauchogourmet.com
has the cheapes t prices for these brands and they quickly get you your order.
If anyone has any questions about mate,I know just about everything on the plant, just send me a private message, and I will answer any questions.