All water softeners work the same. They all use the same resin bed and similar bottles with salt. The major difference between makes is the controls and mechanical parts. The controls are mostly electronic but they still need mechanical parts to move valves, etc. As with anything that moves they eventually wear out or a power surge kills the electronics. What is important is the ease of getting parts and local service if ever needed. Size wise the larger the resin capacity, the less regenerations will be needed.
If you know how to fix things and you can handle any problems, maybe OK to buy online but don't expect any warranty work from a locale company. Buying from a local water treatment company you may pay more and they will install it. Any problems they will usually stand behind their work.