None of the matcha suppliers I use give all that guff about health benefits, they just get on with the business of supplying fine tea.
Best tip I can give you is find a way to try good high end matcha and take in as much of the experience as you can. Remember the aroma and the taste and this will be enough to know whether you are getting decent matcha or not. There simply isn't that much high end matcha around to ever flood the market and lots of the powdered green tea that gets used by the food and drink industry and labelled as matcha simply isn't or is a very poor grade (what I would consider cooking matcha, for flavouring icecreams or cookies etc). The other big problem is that matcha tastes stale very quickly. If you do get hold of some decent matcha, try storing it in an airtight container in the freezer to delay the oxidisation.
Yesterday I had a wonderful opportunity to drink matcha from Uji prepared by a visiting Japanese potter from this area. It was sublime, vaguely sweet with the most subtle bitter undertones. I shared it with my five year old and a friend's six year old daughter, no wagashi was required, both the girls loved the frothy tea and went for second gulps.
For me, matcha is a luxury or a treat, not an every day drink. I find the caffeine hit it gives to be quite potent. I can understand why it has been used for centuries as a meditation tool as it can help sharpen the mind, for those who drink lots of strong coffee I can see how matcha might be considered as a more calming alternative (due to the theanine which can smooth over some of caffeine's effects).
I'd recommend considering a strong sencha if you want to drink green tea regularly for health, if you have the means then perhaps you could try gyokuro (divine). Matcha has a time and place, but, as far as my own life is concerned, it isn't a daily beverage.
If you are stuck for a reputable supplier (or for someone who can make you a good cup of good matcha) you could try this reliable vendor in Japan.
My own supplier is in London but I've enjoyed the teas I've bought from the shop I've linked to
http://www.thes-du-japon.com/index.p...ndex&cPath=1_7
They have a low grade matcha for experimenting with, I would bet that most of the more expensive matcha available in the USA from websites promoting it as a miraculous superfood won't be any better (and could be a lot worse) than this lower grade tea.