You'll be increasing rolling weight, making the bike harder to move and decreasing the bike's handling. The ride quality will go to absolute **** (Have you ever wondered why cars switched to pneumatic tires and, well, never looked back at galvonized?). Also, ever wonder why you don't see a product like this in bike magazines? If you inflate your inner tubes properly, take care of your tires, and don't ride like a moron, you won't get flats that often. And, when you do, you should be able to change the tube on the spot. It's really not that hard - it takes litterally 3-4 minutes at the most if you're comfortable with your bike, and you're back on the trail, road, whatever you're riding on.
Stick with real tubes and just learn how to change the tubes whenever you get a flat. Always inflate to proper PSIs, and you'll be safe from snake bites.
Just my two cents, but stay away from those things.