A neat idea if you have a glue gun permanently plugged in. I've never felt the need for a switch ... but, then, I don't use the glue gun all that often.
There is one part of your construction method that I would do differently - and that relates to your aerial soldering. I would twist wires and leads together (as much as would be reasonable) before applying solder. I would do this for most situations - but most certainly for mains wiring. This not only provides some mechanical connection between the pieces, but it also allows for a larger bonding area for solder to flow through. It is also quicker to solder, especially when you have 3 or more things you want to connect at the one point.
There is one reservation I have, though, and that relates to safety. If the switch were to suffer a mechanical failure, then any exposed metalwork could become live. I do realise that the element is contained within a metal body - but that will have been tested and compliant against the appropriate standard (assuming that the glue gun is an "approved" model). This switch represents a defeat of the double insulation design that is typically used in these glue guns. I would have preferred a switch with only plastic parts exposed to the operator.