I have the same travel charger (but white, instead of black, bought from a 3rd party fulfilled by Amazon vendor). On my charger, you can lock the standard U.S. prongs in a retracted position. Prior to charging your Samsung, push the prongs in and slide the Unlock/Lock to a locked position. That should resolve any possibilities of accidental electrocution.
I do hope your are not involved in safety or risk assessment in any way if your conclusion is that pushing the pins back in is sufficient to "resolve any possibilities of accidental electrocution." What happens if someone accidentally or otherwise moves the button again while it's plugged in, or while inserting or removing the adapter? That big green button is just the type of thing that could attract an inquisitive child's attention. Neither is it beyond the realms of possibility that someone could move it on purpose thinking it was an on and off switch, or think it had to be "unlocked" before unplugging. Bang, pins shoot out immediately exposing the unwary to a full 240V. If that's not highly dangerous and potentially lethal I don't know what it is.
No surprise then that there are no Type Approval or other safety markings on these adapters (apart from a fake "CE" marking which as we all know just means "Crap Export").
The best course of action is to smash this adapter up and put it in the bin, and buy something safe and fit for purpose. If the mains adapter came from a UK retailer, insist that they supply one with a proper UK plug, it's illegal for them not to do so. You never know, someone, somewhere down the line, may just avoid serious injury (or much worse) because you did the right thing instead of trying to save a couple of quid on a bodged job.