“Alternative” can mean several things. You might want a cheaper option, a smaller footprint, a plumbed-in system, simpler maintenance or a different filtration method.
The main alternatives
Countertop RO
Similar technology in a different appliance design. Compare filter cost, capacity, reject water and support.
Under-sink RO
Permanent installation can keep the countertop clear and provide a dedicated drinking-water point.
Activated-carbon systems
Often simpler and cheaper, but the treatment scope is narrower and cartridge performance varies.
Filter jugs
Low entry cost and familiar operation, but generally lower capacity and a different treatment approach.
How to choose
Start with your water objective and installation preference. Then compare total ownership cost and evidence for the claims that matter to you.