While there is nothing wrong with the other answers saying it is currently safe, there is a potential misunderstanding going on. You said you wanted to use it to check if a site is safe, so presumably you will load a page normally after you have found no malicious content when viewing the source. If this is true, then you must be aware that websites are able to detect (or at least infer) that you are using
A potential solution would be to use Inspect Element, which looks at the currently open page and allows for reading the source. This is much harder to detect (though not impossible, since CSS can determine the size of the browser window, which shrinks by a specific amount when inspect element is open). Inspect Element is more complex, and may be more exploitable than
view-source:, so you must apply threat modeling in this situation.