What do you expect them to say ?? That's of no value. They have liability to deal with and want you to buy more tires.
Better is talk to riders that have actually plugged tires and run for distance on them.
Do what you want with your money - let others decide on the facts ..not relying on dealers avoiding liability and wanting you to throw away a perfectly good tire.
Quality string plug kits actually vulcanize from the heat of running forming a permanent bond. After my experience with the plug, and talking to others, I have no issue running a plugged tire for its tread life.
An engineer and incredibly experience distance rider also has no issues with plugs ....stuck one in his BMW in Alaska ( he rides about 30,000 km every year on a single long trip.
He rode the bike home with he plug.
I have a TPMS system tho and if you want to spend money ....that's the ticket IMNSHO.
I got it for the Burgman as the bike brakes and small diameter tires makes checking a nightmare. Moved it over to the Wee.
Very reassuring and lets you see hot your tires get and how they handle at other pressures that you can actually see as you ride.
Found these getting good reviews
4 years now and still works fine.