A. O. Smith AOS-DFRO800
#8 in TanklessFull review
For a household that wants fast, certified tankless RO for less than most rivals. Buyers without a spare faucet should get the brushed nickel version.
Amazon $449.99 Amazon $484.99$449.99
The A. O. Smith AOS-DFRO800 is the better under-sink reverse osmosis system overall, rated 3.3 to 3.1. The A. O. Smith AOS-DFRO800 leads on certification and price. The Frizzlife PD800-TAM4 wins on filter cost. The A. O. Smith AOS-DFRO800 costs $59.99 less ($449.99 vs $509.98).
Frizzlife PD800-TAM4
#12 in TanklessFull review
For a household that wants fast mineralized RO water with low filter costs and does not need NSF 58 certification.
Amazon $509.98$509.98
Prices were last checked November 2, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Which should you buy?
- Choose the A. O. Smith AOS-DFRO800 for certification (certified to NSF/ANSI 58 vs not certified to NSF/ANSI 58; certified to NSF/ANSI 372) and price ($449.99 vs $509.98).
- Choose the Frizzlife PD800-TAM4 for filter cost ($119 a year in replacement filters vs $290 a year in replacement filters).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every tankless under-sink reverse osmosis system; a clear win is highlighted. How we rank explains each one.
| Factor weight | A. O. Smith AOS-DFRO800 | Frizzlife PD800-TAM4 |
|---|---|---|
| Overall rating | 3.3/5 | 3.1/5 |
| Certification 25% | 100 certified to NSF/ANSI 58 | 30 not certified to NSF/ANSI 58; certified to NSF/ANSI 372 |
| Filter cost 20% | 0 $290 a year in replacement filters | 46 $119 a year in replacement filters |
| Water wasted 15% | 50 drain ratio not published (neutral score used) | 95 2:1 pure to drain |
| Output 10% | 71 800 gallons a day | 71 800 gallons a day |
| Price 15% | 54 $449.99 | 44 $509.98 |
| Warranty 15% | 25 2-year warranty | 0 warranty not published, scored as none |
Specifications
| A. O. Smith AOS-DFRO800 | Frizzlife PD800-TAM4 | |
|---|---|---|
| Filtration | ||
| Output | 800 gallons a day | 800 gallons a day |
| Pure to drain | - | 2:1 |
| Stages | 2 | 9 |
| Remineralization | No | Yes |
| NSF/ANSI 58 | Yes | No |
| Other certifications | NSF/ANSI 372 | NSF/ANSI 372 |
| Replacement filters | $290 a year | $119 a year |
| Build | ||
| Tank | Tankless | Tankless |
| Booster pump | - | Yes |
| Smart faucet | No | Yes |
| Warranty | 2 years | - |