Here is a little write up about .co domains and why they are supposed to be so great:
https://www.go.co/about/faq/
Now in actual use I think they are one of the worst domains from almost all extensions.
So lets pretend your company uses the domain name company1.co
The client accidentally punches in the .com and up comes a totally different website.
The client then goes back and tries to enter the domain again but auto complete keeps putting in the .com and the client has to type in company1.co and then hit the space bar or it will again default to the .com.
In my opinion ANY extension even .horse is better than a .co because the mix up with .com will never end and we have not even touched upon the email fiasco associated with the domain yet.