They are expensive is about the only drawback I can list. Been looking at myself. They run about $200. The can handle IIRC about 40L per day and store about 1/3 gallon at any one shot under the sink. If you have opening on your sink and a open electrical outlet underneath then its just a matter of setting it up.

DW went with the electric kettle instead which I think is worthless with a microwave in the house but it may come in handy for trailer camping. Till then she does it in the house. I'd rather have the faucet model.