The whole point about the warning is to give you an informed choice about whether you should install the extension. Presumably some (most?) people don't realise that browser extensions might do more than what the maker tells you they will do.
In theory a malicious extension could, for want of a better word, snoop on your banking/credit card payment/Facebook password... and somehow pass it to an evil hacker. No different really to installing any software on your computer.
How one decides to trust a particular application is pretty complicated. You trusted Google enough to install their browser, why was that?
- Your knowledge of the laws & regulations of your/their country
- Reviews & Ratings
- Some other reason(s)
Should you trust this particular extension and go ahead and install it?
My humble suggestion would be to apply the same reasoning that you used when you installed Chrome or any other application, the fact that it is an extension for Chrome is irrelevant.