Pesonally unless I suspected the engine needed some internal "cleaning" I wouldn't use it in the oil. If you do, dose it up, run it for how ever long you need to and then change the oil.
No point in diluting perfectly good oil, prolly wont hurt it either though.
I use Seafoam in everything else I own (except diesels) for fuel stabilization at the end of the season.
I can compare directly small engines that aren't stabilized, gum up, varnish the carbs, etc.
By comparison, all the small engines I have and all the fuel injected ones, like sleds and boats start and run flawlessly after off season layups (usually a 7-8 month layup on both summer and winter toys here).
I rarely use it or any other products during normal operation. Once in a while I get the urge to give Autozone an extra $10 an get some injector cleaner or diesel perf additive, but not often, and not sure why as I've never seen any difference by adding to a well maintained engine.
'06 X2 MCX
"I understand why some people may not want to do this the way I have recommended but I can't understand the death grip some people have on a toilet plunger with a hose fitting." -JimN