So speaking only for the workspaces that Remote Year had in each city, security was adequate where I would leave my laptop setup while I went to lunch. There will almost inevitably be other people working and keeping an eye on your stuff. I do recommend that you setup hot corners so you can easily activate a screensaver which locks your computer when you leave. I know there was one incident over the summer at WIP workspace in Lisbon while I was there where someone left their computer setup overnight and it got stolen. I would recommend packing your stuff up at the end of the day and taking it home but I left my laptop in each workspace for lunch without issue everywhere we went.
For more security-related advice see Days 6 and 7 on Infosec.