Are the Repair Shop Engine Cleaning Services different than the Over the counter Additives?

No its the same stuff that is avalable over the counter but I wouldn't recommend adding it yourself unless you change your own oil because basically what it does is breaks down the oil in your motor so it would be like driving your car around with water in it instead of oil. In the shop I use to work at we always ran the car for a max of 5 minutes so if you plan on adding this to your motor then driving to the service station good luck