There are many cases where you're getting blood drawn already and if adding another test onto that is inexpensive, that's a pretty convenient add-on. That's useful for many reasons.
I was also wondering how it performed compared to a stool test, so I looked it up, and found "While the blood test caught 83% of the cancers found by colonoscopy, it missed 17%. That’s on par with stool-based tests."
And will combining the two tests catch a higher percentage? Could go as high as catching 97%, although I suspect lower due to some correlation between what cancers the two tests will pick up (eg. not advanced enough to leak blood into stool may equate to not advanced enough to leave markers in blood). But it will also increase chances of a false positive.
I was also wondering how it performed compared to a stool test, so I looked it up, and found "While the blood test caught 83% of the cancers found by colonoscopy, it missed 17%. That’s on par with stool-based tests."