My radiator is leaking pretty badly and needs replacing. It usually doesn't seem to leak until it builds up pressure and then after you shut it off it keeps leaking for a few minutes then stops.
Agreed. Money would be better spent making a proper repair here. The stop leak stuff has the possibility of causing more problems and thus more money spent in the long run. Do a good inspection of all cooling system parts and do it all at once if other things are needed.
I would maybe carry stop leak in a trail kit where getting off a trail is paramount and perhaps JB Weld or duct tape haven't worked. As an alternative to a proper fix, not a chance.