Still, I think that the point is to not take (any) chances...
IMO it depends on the amount of coins.
The the amount justifies destroying a 70$-100$ device, sure. That's the best way.
If the amount however is not large enough, "trusting" in the security mechanisms of the manufacturer as well as overwriting the memory yourself is a very good alternative.
Especially since that is the same what is being done with hard drives which contain sensitive data. Whether this is as easy achievable with a HW is a different story tho. If so, there speaks nothing against doing so. If not, then destroying it would definitely be the better choice.