I would NEVER use such a product!
All of the above responses are spot-on! They can do more harm than good with the exception of adding MMO when the level is down prior to an oil change.If you have concerns about sludge and its effect on your engine due to prior care,pull a valve cover and take a look,but otherwise I would just practice good maintenance and keep an eye on things...I am able to run Valvoline to 5k on oil changes now with a Purolater gold filter-but all my miles are long.