We purchased our Keiser M3i about 4 months ago and have logged ~1100 miles so far. Overall I would say this is a very solid piece of workout equipment. Neither of us are very large but I would fully believe the weight rating and it seems like it should last a long time. There is plenty of range on the resistance.
I had never used a spin bike prior to this purchase. My wife had and she likes it as much as the bikes she used to use in class. Personally I was surprised/happy with the comfort. I didn't use to cycle much; just limited use of traditional exercise bikes and some mild use of my commuter bike - I was prepared for the worst. From day one however I was able to get a good position and never have had an issue.
We purchased the bike to use along with the Peloton app and love the combo so far. We debated quite a bit to go with the Keiser or the Peloton bike but in the end decided the higher monthly subscription cost and potential replacement cost/obsolescence of the built-in display outweighed the feature of competing in class. The computer on the Keiser makes it easy to follow along with cadence and importantly resistance instructions. While it obviously doesn't match 1:1 with the Peloton it's a huge advantage to have a digital number to track yourself against instead of just a knob as available on most other bikes.

Why 4 stars? I have a few nitpicks:
* "Feel" - There are some swaths of resistance/cadence where when seated I think you feel the magnet applying resistance or some other grit every few strokes. There is no grinding or anything like that, just something noticeable. Doesn't impact the workout/resistance feeling but I didn't notice this on LeMans Revmaster I had to use for PT. I wonder if it is a product of the lighter flywheel (which is great for the knees).
* Noise level - Make no mistake, the bike is not loud at all - we don't hear it elsewhere in our house or over the classes we're listening to. It's just that Keiser advertises it as near-silent. Of course this is a subjective statement but I wouldn't call it that. I think most of it is due to air from the flywheel reflecting off the plastic housing. The LeMans Revmaster had an open flywheel which "seemed" quieter, but tough to make a direct comparison in their respective environments.
* Minor cosmetic defects - none of these impact use but the computer housing has a scratch on the inside, the water bottle holder had a chip and there were scratches on the flywheel. None of them are a big deal, just not expected for a $2000 bike.
* Tools - Would have been nice to have the required tools included.

Overall I'd definitely recommend the bike and hope to use it for many years.