The bikes are about the same price, but the Keiser screen is a simple LCD display that's much cheaper to replace if it gets broken and is fully usuable without a subscription.
Plus, I think the bike looks better.
When I'm considering buying a smart device that I'd be uncomfortable throwing away if/when the company ceases support, I ask them beforehand: Is there an open API and/or SDK? Does code or protocol escrow exist? This saved me from buying a smart watch and a smart ring. The manufacturers seemed healthy at the time but were bankrupt or acqui-hired and shut down within a year.
"It's a $2k training bike. You could spend $1k and get a really nice brand new road bike and a smart trainer that controls resistance like a Wahoo Kickr Snap (or several others) for ~$500."
That being said the M3i seems to be one of the more flexible options if you are gonna go the stationary bike route.
I have a really nice road bike, and a decent steel framed commute bike. I've used both on a trainer, but it's not the same feel as a spinning bike, particularly when standing up and cranking hard on the pedals.
A good spinning bike will last a decade or more with little maintenance, but you'll be changing tires often on the road bike trainer as well as all of the other maintenance that comes with a bicycle.
You can get a good workout on a bike+trainer and if that's all your budget (or space) allows, it's a good option, just don't expect it to be a spinning bike.
I haven't actually tried pairing it to my iPad or other devices.