Quick take
Frizzlife PD800 is the closest tankless capacity competitor. RKIN U1 is the better no-install premium alternative. Traditional tank RO is the value alternative if standardized parts matter more than compact design.
Closest like-for-like: Frizzlife PD800
Frizzlife PD800 targets the same high-capacity tankless buyer and adds a remineralization option in TAM configurations.
Best no-install alternative: RKIN U1
RKIN U1 moves the treatment to the countertop and adds hot/cold dispensing, but costs more and uses appliance-style proprietary cartridges.
Best low-cost architecture
A traditional tank RO system is less compact but often cheaper to repair and easier to maintain with standardized components.
How to choose
Compare finished-system certification, annual filter cost, required flow, available cabinet space and whether permanent plumbing is acceptable.