I've used the tyreweld, it worked twice when the tyre had a small hole, enough to get me to a tyre place at which point I got a new tyre. ( just my personal preference )
The third time I had to use it, it didnt fix the hole, mind you the hole was huge so I had to use the "Fizz's dad with a van" breakdown recovery service
Personally I prefer the Rep and Air Kit from Hein Gerricke, as it'll cope with a large hole in the tyre than the Tyreweld stuff does.. and it takes up less room than the can of tyre weld does under the seat hump.
I guess using it with the rep and air kit, would probably work OK though if the hole was massive. I'd wander how the tyreweld would react with the glue that holds the plug in on the rep and air kit though...