Quick take
RKIN U1 is the premium hot/cold alternative. Waterdrop K19 is the value countertop alternative. AquaTru is the evidence-first alternative. Under-sink RO is better for permanent high-volume use.
RKIN U1
U1 costs more but adds a more complete hot/cold appliance experience.
Waterdrop K19
K19-family models are often cheaper and simpler if hot-water features are not central.
AquaTru
AquaTru is strong for shoppers who put model-level third-party certification ahead of appliance features.
Under-sink systems
Homeowners can get faster ongoing kitchen flow with Frizzlife or Waterdrop tankless under-sink RO.