So it doesnt really matter they are eating potatoes. Unless they want to do it cheap then it makes sense. Which is good but there's so much more variety in the keto approach then boring potatoes.
People lose a lot of weight this way. Insulin sensitivity increases. Insulin-lowering medicines can be reduced or stopped. Bad cholesterol drops to the floor.
If you go beyond monomeals of potatoes and add in tasty vegetables (like you do in keto) and limit the fat you add to the meal, you will have all the benefits of the potato diet without the mind-numbing boredom.
Variety in the keto approach? There are only so many ways to dress up chicken/beef/pork and cheese.
Doesn't get much more varied than that for a 'diet'.