I purchased a medium sized red version.  The vender was Buycostumes - fulfilled by amazon.  The shirt was authentic and exactly as described.  It came with the attachable communicator pin (plastic) and 5 attachable metal pips.  The shirt is polyester and very well crafted.  Looks VERY close to the exact shirts used on the show.

The medium shirt will be worn by someone 5 feet 10 inches, 150 pounds.  It fits almost perfectly.  The sleeves are just slightly long.  The chest and waist area fits fine.  The length is short - just about belt level.  If you stretch or reach, the shirt will rise to about navel level.  This is as designed - modeled perfectly after the shirts on the show.  But because of this, it is necessary to wear a shirt underneath - preferably black.  It will be necessary to pull the shirt down over the belt line often after standing or reaching.

I am very pleased with this purchase.  Add a black t-shirt (I bought a black Champion Men's Double Dry Training T-shirt.  It's perfect) and a pair of black pants, and you'll be just like the Star Trek character.

The authentic version I received is trademarked 2011 CBS Studios Inc. and crafted by Rubie's Costume Co. Great quality with the plastic communicator pin and the metal pips.