I don't own one but I used a home made on once for beef ribs. Only once and that was the last time.
Heres some good pro & cons
Pros:
Sounds cool, and oh so French.
Prevents waste.
Prevents overcooking.
Two words: portion control.
Three words: internal temperature control.
You can train a monkey to do it.
Preserves flavor of fruits and vegetables rather than having flavor and nutrients wash away in the cooking liquid.
Cons:
You can train a monkey to do it.
It’s unnatural — you’re cooking food in plastic for chrissakes!
Alters natural flavor and texture of food.
It does so by altering the natural exchange of heat and fluids inherent in any cooking process.
It turns to seafood to mush.
Beef becomes some odd, never-before-seen-in-nature form of medium-rare throughout the meat (not just the center), and attains an odd, compressed, texture.
Marinates the hell out of whatever has been so encased.
Nothing gets crispy, browned or charred. (Chefs will tell you they “finish” things under a broiler, but it ain’t the same thing.)
Finally, the biggest con: YOU’RE PAYING TOP DOLLAR FOR FOOD THAT’S PREPARED THE SAME WAY AS BIRDSEYE AND STOUFFER’S!