Cost, however the old saying is true - ya gets whats ya pays for!
I have owned a Mini Vivaldi about a year now. I am totally pleased with the unit and the support from Chris Coffee Service. I had an issue with moisture in the boiler/group gauge which was quickly resolved. I added the progressive pre-infusion about a month ago along with some Ikea LED lights so I'm set for now.
This is a non-plumbed model and I have been pleasantly surprised at how easy it is to maintain. For a single group unit, the build is superior to most of the competition. My coffee-loving friends are envious. Highly recommended!
Chris Coffee Service is great to deal with - both before and after the purchase.