I use the type plugging kit you have all the time. You're not likely to have any problems with it unless you pick up something large and the plug just won't fill the hole. As for the rasp I never use it, sometimes it takes lots of pressure on the t-handle to force the plug through, but you don't have to worry about leaks.
I too work at a shop that does repairs. we use the plug/patches pictured above. I've fixed dozens of tires with the external plugs that were leaking. seen a few that were fine but all by the same farmer. Never had a customer come back that I know of in the year and a half I've been there.
been to a shop that did external repairs like you guys but we're not gonna go there. that was the least of the issues there.
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"