My mom has a land line with only local calling to save money. Years ago I created several GV numbers, so she could have a local # to call all the kids.
I put an obi there for when I visit. She can not hear well. We got her a CapTel with speech to text capability phone so she can read a captioning of the conversation.
Today her internet is out, so the CapTel is down. If an Obi was her main phone, that would be down.
Long story short, I would not depend on an Obi type system for an older person, unless you live in the same town, and can easily troubleshoot.
She has a also has a phone system that plugs into a regular phone jack and that system comes with a desk phone, a cordless phone, and a pendant type phone. She can understand the pendant type phone sometimes.