We used this 'Sweet Inn' service for the first time and unfortunately it wasn't a good experience. It is already annoying enough to be forced to install another App on top of Airbnb but...whatever.
Anyway, we got a 'smart apartment' with a 'digital key', whatever that is, that was supposed to be sent to us 15m prior to check in time. We didn't get any key and we waited outside the entrance for 50m until a guy came and opened the door for us. I understand that there has been some issues in another place, etc...however this was our experience.
If that wasn't enough, that same night we went out and got back around 11pm just to discover that the code to enter the door wasn't working anymore. We called the guy that came in the afternoon and he didn't know what to do. After some time a guy exited the building walking his dog and told us that the codes do not work after 10pm and we need the typical black pad to enter, which we weren't given. So, in practice, they got us into a place where we couldn't enter after 10pm without letting us know (Ok, I reckon that was by mistake, but still). We were lucky the guy was walking the dog out at night and let us in. But I could easily imagine going back late at night and just be stuck outside the building.
So that was our check-in experience. Besides that, the place is ok and it is in a great location, it was not particularly clean (the floor tails in the kitchen area were sticky) but acceptable.
I would recommend staying in this place in general, but the check-in + being stuck outside in the night experience was unacceptable for an organised service which I suppose is what Sweet Inn is trying to provide.