I own a Key, it replaced a Niche. Been using it for four months now.
The espresso from the Key delivers more flavour notes. The variable speed makes a small difference too - lower speed a bit more clarity, higher speed a bit more body. I’m no expert, but the grinds out of the Key are visibly different than from the Niche, it was the first thing I noticed.
Same bean selection on both grinders. Same prep. Obviously the Key does its Magic Tumbler stir, but I RTD again anyway.
I find the Key easier to clean. I prefer the slim footprint, and it’s quieter. But most of all I prefer the espresso.
I’m not overselling the Key, at this level there can’t be a big difference, but it is noticeable. If I was offered a refund for the Key and given my Niche back, that’s a deal I wouldn’t take. You pay your money and take your choice.