I have two of them and I like them a lot, but they are not perfect.
Positives:
Unless your outer shirt is skin tight, no one can tell you are carrying.
They hold the gun securely.
They are great for driving trips because your gun is far more accessible when you are behind the wheel than it is in belt or pocket holster.
They seem to be well-made.
If you have a snap-button shirt, you can reach your gun fairly easily whether you are sitting or standing.
You can wear a gun on either side, or both.
Negatives:
So that the gun is held securely, it must go all the way in to the fairly deep pocket/holster, thus slowing retrieval. There are a couple of velcro tabs to secure the opening. I once tried to position my M&P 40c so that the grip was held more accessibly between the tabs, but the first time I leaned over, the 40c slid out.
From a standing position, pocket and belt holsters will provide quicker access.
They are expensive, around $60.
Positive or negative, depending on your preferences:
In the most secure position, the gun is almost directly under your arm. Thus you feel it frequently when you move your arm. Some people may not like that. I do.
They can be hot. On cold days, they will definitely supply an extra layer of warmth. On hot days, they will ratchet up the perspiration factor. I always wear a cotton undershirt under mine, as it helps with air circulation over my skin. I wore mine on a one hour walk in 85 degree temperatures last summer, and I was not uncomfortable. However, I would never wear one directly against my skin.
They are tight. To hold the gun securely against your body, they are made out of a tight-fitting lycra-spandex material. Some may not like the feeling, but others will find it supportive. Personally, I think it enhances my already manly physique.
Hope that helps.
