Safety Seal, Speedy Seal, and other brands that use the concept of rubber ropes stuck into the tire through the punctured hole, with the idea that they will create a knot of material against the inside of the casing, and won't pull out. This works better in car and truck tires that aren't subjected to the same forces as a Motorcycle tire that flexes far more as the bike leans from side-to-side.
To be fair, the failures I've seen were mostly young guys on Sportbikes riding fairly aggressively, who might have a more difficult time affording the steady diet of tires for their bike, so were more likely to plug a punctured tire and keep riding. A relatively slow Cruiser, or any bike ridden moderately, won't place as much stress on the tires as those subjected to high acceleration, cornering, and braking forces. Still I'd consider any of the rope plugs to be a very temporary get-me-home-riding-gently measure.
If someone really wants to plug a tire, I'd strongly suggest the combination plug/patch which is fitted from the inside of the casing, with the tire dismounted from the wheel.
Any plugged tire is considered compromised, (even the plug/patched tires) and no longer carries the same speed or load rating, according to tire company engineers I've talked to. Now of course they want to sell tires, so that position makes sense from that standpoint alone. But I had one explain it this way: Once you poke a hole through a tire casing, numerous belt fibers or wires are destroyed at the site of the injury. This can only weaken the tire. How much it's weakened can only be determined by dissecting the tire at the point of injury.