We installed the Kohler version of the walk-in tub for our daughter when we built our house. Fifteen years ago, Kohler was the only brand we could find. It is standard tub size. She has cerebral palsy and it was the best answer for her to independently get in and out of. She also likes to soak in warm water to loosen tight muscles.
Her tub has a gasket seal that activates with electricity when the door is opened. You get into the empty tub before filling and wait for the water to drain before you can get out. Our electricity went out one day when she was in it and the tub leaked.
We must have had the only one of these tubs in our area for a few years. The plumbing distributor didn't have one on display, so they called to see if they could send potential clients over to see it several times. Both ladies, who had arthritis, were so eager to try it out because they wanted to soak. However, they both found that the seat was too low for them to stand up.
If you have assistance in the house, you could install a doorbell or intercom to summon help if something happened.