A. O. Smith AO-US-200 2-Stage Under Sink vs Frizzlife MK99

Only the A. O. Smith AO-US-200 2-Stage Under Sink is certified to reduce PFAS, chloramine, mercury and microplastics and 1 more. Verdict: the A. O. Smith AO-US-200 2-Stage Under Sink for broader certified protection (8 vs 3 of the contaminants we track); the Frizzlife MK99 if running cost matters more. Replacement filters and water for 2 people cost about $168 a year on the A. O. Smith AO-US-200 2-Stage Under Sink and $40 on the Frizzlife MK99; they cost $140 and $70 to buy.