How to choose a walk in tub?

Given a choice I would go for a Zero Entrance or Roll in Shower and not a Walk in tub.
At some point even a walk in tub may not be possible.
A roll in shower can be used at any time and it can be used by anyone at any stage.
Appropriate Grab Bars for when a person is still walking and the shower is large enough for a Shower Wheelchair or a Hoyer Lift. And it is large enough for helpers to aid in giving a shower.

As to the walk in tub...not sure how I feel sitting in a tub as the water empties getting cold until I can get a towel around me. And the ones I have seen the "door" opening is rather confining so if there are mobility problems it is not easy getting in and out.

I HATE walk in tubs.
You have to sit there and wait to fill up the tub. When you are done, you have to sit and wait for it to empty. You have to shore up underneath because they weigh more than normal tubs and put the weight at an awkward concentration.

My folks wanted one in their bathroom, so we did it. They just used it as a shower with a seat instead of a tub...waste of money.
Crazy story... one time my Mom was sitting on the seat area and slipped into the lower area. Luckily it wasn't full of water, but she got stuck, and I had to call rescue services to help me lift her out of that area because the door opens inwards.

I did some research on these about 2 years ago. My conclusion was that it uses a ton of water (expensive), the senior has to sit in the tub and shiver waiting for it to fill up, then has to wait in the tub and shiver while it drains completely before you can exit it. Takes a long time to complete the bathing process. So, unless the designs have improved, I wouldn't go this route.

I vote for a zero-clearance roll-in shower stall if at all possible. This will not be an unwanted feature when selling the house like a walk-in tub would be.

And I agree, at some point the tub may not be able to be used by the senior if they can only get around in a wheelchair.

This is an after thought advice when it comes time for your Mom to sell her house. If she lives in a 55+ community, no problem, enjoy. If she lives in a regular subdivision or city, the next buyer of said house [young couple with small children] may not want a walk-in tub, so there would be a cost of removing and replacing with a regular tub/shower, or lowering the price of the house by that cost. Just food for thought.

Wish bathtubs/showers would come with a "self-cleaning" option.

One of my friends had one of those tubs installed about 10 years ago. She immediately regretted it - said the jets made her sore muscles even more sore - and said it was a lot of upkeep. She misses her shower.

My dad had a number of fellow senior friends who put these in their homes. All ended up hating home in a short time afterwards. They sat cold and shivering waiting for it to fill and then again after a bath waiting for it to drain. It took a lot of water and took so long it wasn’t worth the time or expense.

We haven't had a lot of talk on the forum about this for a long time,🤔 From what I can remember the people who loved their walk-in tubs made sure to get extra large drains so they emptied faster, another bit of advice is to look for models that allow a caregiver to easily reach inside to assist. And of course these appeal most to the people hate showers, and especially love soaking and using jets.

One other thought - for much less than the price of a walk-in tub and installation you can get a very nice bath lift for your regular tub

Different perspective... my dad had been disabled by a stroke. He preferred baths, so my parents got a walk in tub. My dad used it every day for 15 years, included the jet massage feature. Both my parents preferred baths, so my mom used it also (sans jet massage). She has mobility issues from a large lymphodema in her right leg from cancer surgery way back in the day. For my parents, it was a great choice because of their preferences and mobility issues. I didn't care how it affected the house sale... they had upgraded 0 items from when they built it, so it wasn't an issue to me. It all is added to what goes for mom's care now, and that is what's important.

My friend had one of these installed for her parents. They had a home with one bathroom, so there were not a lot of options--(It has been some years since they did this--I'm sure I'm not up to date.)

The DH of the couple LOVED the tub, although they had to install a new water heater AND the tub used every drop of hot water to fill. The wife hated it--it took so long to get bathed! So I know they went back and installed a shower head, for her, and also for him to use to be rinsed.

After the death of the parents, the kids couldn't sell the house--the bugaboo? That tub! With only ONE bath, it was actually a pain for any young family, and that's who was looking for a house. The family ended up tearing out the step in tub and replacing it with a 'regular' one. I know my friend said in the end it ran them close to $20K. And they did most of the work themselves.

I'd opt for a 'jetted' over-size tub and put in plenty of rails, etc. The home we bought has a very deep tub and my DH LOVES a long soak. I am a shower person, only, can't remember the last time I took a bath.