A single data point, FWIW: A couple of days ago, I spent a night at the Aloft Bangkok. Two dispensers on the wall in the shower, one for combined shampoo/conditioner, the other for shower gel. Both were spotless, no mold, either. The tops were locked, you need some type of key mechanism to open them. Obviously they aren't completely tamper-proof, but the point isn't to make them into bomb-resistant containers. The point is to discourage the casual miscreant. Anyone who is really determined can break them open, but I see someone that determined going for a bigger target than the shampoo dispenser in an individual room in an Aloft, fundamentally a lower priced chain.