It generally works ok. Lots of annoyances though,.
1. different workspaces don't separate different extensions. So you don't truly have a distinction between workspaces. Do I want a workspace for web dev work? Why should I have all my shopping/coupons extensions enabled on that workspace? And if I'm studying - I definitely don't want shopping extensions on there. Nor do I want my CSS editors or my download managers. Workspaces are only halfway done.
2. None of the search engines are imported from chrome, meaning you have to enter them all manually again. And that means visiting each and every site and performing a search and copying the part of the url for the search and entering the name of the site and entering the name of the shortcut and pasting the url and adding "%s". for-every-site!!
3. Annoyingly, they've remapped ctrl-tab and ctrl-shift-tab to their own special snowflake tab switcher which does not do a switch in order of tabs. Instead you go through tabs in order of last touched-tab. If you're going to mess with a known paradigm, at least make it optional! ctrl-tab is basically semi-random now and that makes it semi-useless.
4. You are are forced to use their new-tab page. You can't set it to an extension or even to a web-page. The sidekick new tab page brings ZERO VALUE. You can search from your address bar - you don't need a new page. you can access your "apps" from your side bar, you don't need a new page. So they disable the ability to make the new page actually useful and force you to use their useless one.

Right now, Sidekick is slowing me down more than anything. Perhaps with time, it'll make me more productive, but these annoyances are stacking up.