Holts tyreweld has been designed as a temporary repair in order get you home/to the garage, and is only recommended as such by Holts.
Holts Tyreweld is the only Tyre sealant on the market to recieve endorsement from the National Tyre Distribution Association (NTDA), this is due to the product being a water based latex emulsion.
Which can be simply washed out of the tyre using warm soapy water, and then following British Standards for tyre repair (AU:159) any dried remnants can be removed with a buffing wheel to ensure good adhesion of the repair patch.
Regarding permanent repair, Holts have an agreement in place with all 205+ National Tyre & Autocare branches (who are the second largest tyre repair company in the UK) to repair any tyre treated with Tyreweld for an additional small surcharge for the added labour time - provided the puncture damage is not too severe.

The Holts Tyre Weld can be used on virtually alll cars

We imagine that the Smart vehicle originally came with the manufacturers compressor puncture repair system where the inlet of the valve is removed with a tool & then inflated with a compressor hooked upto the the nozzle on the product opens up the tyre valve automatically & it has a propane/butane propellant which inflates the deflated tyre. The instructions can be confusing specifying the ideal scenario of 10 to 2 connection and the puncture positioned at bottom of tyre. The latter being the most important of the two so that the puncture is in contact with the ground and therefore does not allow any of the formula to escape during inflation

It would depend on your van and tyre size. Please visit your local Halfords store where they can advise you further

Unfortunately, Holts Tyreweld is not suitable for use with wheelbarrows.

Holts Tyreweld can be used with your trailer but please remember that this is only a temporary repair.