I have used 4 plugs. My current tires have 2 plugs (unusual) without problem. The other two worked problem free for lots of miles until the tires were worn out or the car was traded.
The area that a tire place will patch is shrinking. For H-rated tires the "patchable" area is much smaller than for T-rated at many/most shops. In three of the cases, the a tire place had said the hole was too close to the edge of the tread. That is the reason many places offer free patching: in most cases I predict they say the tire is not reparable and try to sell 1 or 4 new tires. In the other case, I did not take it to a tire place, but just fixed it in the driveway. A spray of maybe 10 to 20% dish washer detergent found that slow leak for me.
Regarding Safety Seal, the tool is nice, but the plugs are different from the ones in most stores. The plugs are self vulcanizing; there is no cement. Black Jack are also respected self-vulcanized plugs.