It was very nice to drive: very stable and rather fast and i did 2x20km/day to work. However its bigger weight compared to a simple bicycle makes it not suitable to mountains
Is there any recommendation you could provide?
In EU (FR/CH/DE) there are specialized forums about them and I bought mine second hand. You'll love it !
It's in German, but you can ask questions in English and they will usually be answered in English as well.
As for your question about which models are well designed, I'd say that if you're looking for speed, the fast ones are the Milan SL, the Alpha 7 and the upcoming Snoek, but those are not suitable for tall and/or wide riders. If you don't fit into those, your best options for speed would be the Milan GT, the DFXL or the upcoming Alpha 9.
If you're rather looking for something more practical, the Quattrovelo is the way to go; it has four wheels and therefore a bigger and more usable luggage space, which can even be used to transport a small child.
It is probably a good idea to do one or more test drives first, so you know what you are getting into and what is important to you.
I bought an electric bicycle instead :-)