1) We don’t really recommend it.
2) The .co domain name is often marketed as a good alternative to .com, primarily for use when the .com domain name is taken.
3) The problem with that is that it is confusing. Some people are likely to think it is a typo. Others may simply mistype it, adding the “m” and ending up at someone else’s website.
4) It also communicates, to some internet users, that your site is low-quality — it carries the feeling of “knock-off,” like those unlicensed cartoon character performers in Times Square.
5) Even if you can’t get the exact domain name you want, you’re almost always better of with a .com the .co domain name.
