And just like air-con installers, they will insist you buy their cheapo circuit breaker even if your house already has one.
I would suggest buying from ACE Hardware or Handyman as they have direct contact with the distributor in case the unit goes kaput. Their stocks tend to be newer too (especially at the malls) and there likely is a 0% installment option if you're buying using a credit card.
Just be mindful that the installers need to be watched over, in case they screw up your tiles or the drainage in your shower. If your shower area already has provisions for a wall outlet, you'll most likely not need to get the circuit breaker they are bringing with them. They will insist that it isn't safe without another circuit breaker, but that's BS. My analogy for it is that it's like wearing a second condom on top of another.