The three-wheeled model has been very useful because it allows you to concertina the walker when you go into shops to let people pass by you in the aisle. Shops also often have very narrow aisles because the operators frequently put out special product display islands that take up space there. So the three-wheeled walker was useful for mum in the early days when I used to take her out to do shopping, such as when we went to the bookstore. Mum appreciated being able to get her device out of people's way quickly so as to avoid embarrassment and inconvenience. In the nursing home the hallways are wide because they are designed for the use of these kinds of devices, so there is no need to economise on space there.
The three-wheeled type of walker is also convenient because it is able to fold up flat making it highly suitable for transportation in a normal car. In fact mum used to keep a walker in the car all the time, and used it when she went out shopping with her housekeeper.
But the physiotherapist said that the three-wheeled walker was not stable enough to support mum's weight. Mum is getting quite frail and the three-wheeled model can't be relied upon like a four-wheeled walker would. So I brought the three-wheeled walker home this afternoon to put it into retirement and it is now sitting in my storeroom among the boxes of stuff taken from mum's apartment on the Coast. (I am slowly going through these boxes that dad filled up over the years mainly with papers. I have been going through these boxes since November and there are still quite a few more to process.) So I might even put the three-wheeled walker on eBay to sell it because I don't envisage a time when it will become useful for me. Not right yet I think.