Are pedal exercisers any good?

I’m thinking of getting one of these for my mother. She’s a somewhat large lady - about 20-30 kg over her ideal weight - and walking too much and too regularly causes her some knee pain. I read that mixing up walking with cycling would help increase the amount of exercise she could get in before hitting the pain limit. Pedal exercisers seem like an ideal thing to use. She can keep one in front of her couch and use it while watching tv. I wanted to check with the dope if this is indeed a workable/good idea, and if y’all had any specific models to recommend. The link above is just one of the first few that popped up, I have no attachment to it. Bonus question - Why do a couple of the models on that page cost more than a 1000 USD?

It’s a good concept but the key questions are if she’s motivated to use it, and if she will use it.

They are excellent and it is great to do something that takes no thought while using one EVERY SINGLE DAY for about 3 weeks to get into a new habit.

Well, I figured I’d get it first, and then I can try and make her use it.

Thanks, you sound like you’re endorsing it? But the latter part of your sentence confused me a little. Anyone have any ideas on where I could get one in the NYC area?