Earlier quoted context omitted.
I have not used CreditKarma's tax product, but I've heard folks say that it calculates some things incorrectly. I think that's understandable for a brand new product, but I'd be cautious about using it this year if you don't (1) have a very simple return, (2) check their work against the IRS forms/instructions and/or (3) check against another product. (For those who don't want to give TurboTax or H&R money, I've been…
I haven't used CreditKarma's tax product either so I can't speak to its accuracy, but from my understanding they didn't build their own product, they acquired a company called AFJC which has been in the online tax space for a while.
Credit Karma missed some things in my NJ state return that would have cost me a couple hundred dollars. There didn't appear to be any way for me to manually include a correction, so I ended up filing with TurboTax (free version).
This wasn't even a particularly esoteric exemption, I expect it would have come up with anyone who worked for two different companies in the same year. Aside from that, I'm a very standard case.