My experience with Slime has been limited to bicycle tires, where the product does a good job sealing up pinhole and other small punctures in the tire tube.  I have never used Slime in an automobile tire, but since the materials are basically the same, I would assume that the product would work in a similar way.For an automobile, where the flat occurs makes a big difference.  If your car is parked and notice your tire is flat, this kit would probably be quite useful.  You can at least use the compressor to pump up the tire and check how bad the leak is.  If it is a fast leak, you can try using the Slime and see if it takes care of the problem.  The car does not need to be jacked up to use the product.If the puncture happens when the car is being driven, the problem is more serious.  When you drive on tire that is significantly deflated or flat, most times you will do heavy duty damage, or tear the tire.  If that happens, Slime won't help.  The tire will need to be replaced.  The instructions state that Slime will not work on punctures greater than 1/4 inch.  So basically, Slime is intended to address only minor tire damage.The Smart Spair kit is a pretty good deal.  It consists of a 16 ounce bottle of slime, and a compressor which plugs into the lighter outlet.  According to the label, a 16 ounce bottle, should be adequate to treat one averaged sized tire.  The 16 ounce bottle is available at Amazon for about nine dollars.  Subtract this cost from the price of the kit, and you are getting the compressor for less than fifteen dollars, which is not a bad deal.  The compressor has a pressure valve, ten foot cord, and on/off switch.  It is pretty noisy, and seems to have a reasonably quick pump rate.  It is rated for use on a minimum 15 amp circuit.  Some older cars have lighter circuits rated at only 8 amps, so you may want to check this before you buy.Hopefully I will not have to use the Smart Spair.  Based on the good (though limited) experience I have with Slime, I thought it would be good to have around, just in case.  There are many situations, where changing a tire at the side of the road, can be hazardous.  A kit like this could be valuable to those that are not capable of, jacking up their vehicle and changing the tire.  It does not take a mechanical genius to follow the directions.