I tried. Had a few sections where I wasn't clear how it was working and the refund was not adjusting as I expected it to as I entered new information. Also it required me to itemize a charitable deduction when I shouldn't have needed to (you only itemize if one specific item is $500 or more, not if your total donations are $500 or more) and then it double counted that deduction and I couldn't delete the itemized line. A few quirky things like that.
In the end it said I would get a refund of ~$2,850. Then I did everything myself and got a refund of $4,350. The worst thing is CK doesn't show you your forms or schedules so I can't track down the discrepancy. I contacted CK customer service about a couple of my issues, including whether or not I could see my actual Form 1040, and they gave me some stock answers that were not helpful. I was excited about this because I love CK for credit monitoring. Unfortunately this product isn't quite ready for prime time yet.
(I think the biggest difference is coming from CK's treatment of my HSA distribution. On CK's HSA form there was no section for "Qualified medical expenses paid using HSA distributions". So I believe they were taxing me on my distribution and adding the 20% penalty. But that doesn't totally resolve the discrepancy)