These holsters are definitely legal and MA doesn't specifically have any laws regarding types of holsters.

That being said, you should not buy or use that holster, since it doesn't cover the trigger and trigger guard, which is one of the primary functions of a holster.

You will not be able to pull out and properly grip/aim your gun while in that holster better and faster than you would using a normal pocket holster like this one: http://www.amazon.com/Wesson-Bodyguard-Comfort-Designed-Holster/dp/B00P9RVHFQ , which also will make your gun look and print like a wallet.