Quick take
RKIN U1 is the premium choice for hot/cold dispensing and feature depth. Waterdrop K19 is the more value-oriented choice when purification and a smaller upfront commitment matter more.
Feature tier
RKIN U1 behaves more like a premium water appliance, while K19-family systems emphasize purification and countertop convenience.
Upfront cost
RKIN U1 sits near the top of the countertop RO price range. Waterdrop K19-family models generally cost substantially less.
Filter ownership
Both rely on proprietary cartridges, so replacement price and availability should be part of the buying decision.
Best fit
Choose based on appliance features first, then certification scope, annual filter cost and counter-space requirements.