I gave Credit Karma Tax a try this year. I mostly liked it, but did find one serious deficiency compared to others I've used. It did not handle the deduction for state income tax nearly as well.
The IRS allows deducting either the actual sales taxes you have paid, or you can use a standard amount based on your AGI and your state and local tax rates.
Most other software I've used knows about this. If you enter your actual amount (or 0 if you do not know the actual amount) they compare to the standard amount and go with which is higher.
CKT just goes with what you enter. If you ask for help on that item it doesn't even mention the existence of a standard amount. It just says fill in the amount you get from adding your receipts.
No data obviously, but several people in my group have mentioned that they ran into (software) bugs with your tax filing software. You might want to look into that. I love your service, so I hope the tax service takes off as well!
I've looked at Credit Karma tax free, but I'm a bit nervous as I own a California LLC (100% sole owner), and also have capital gains, dividends, write-offs.
Is Credit Karma a good choice for more complicated returns? Last year I paid H&R $650 for literally one hour of time which infuriated me.
I just did my taxes with them, and it does have some support for business income and loss, so I think in your case (pass-thru entity) you may be okay- I didn't have to use this section this year as all of my income came from my salaried position this year, so I can't ssay for sure how it works.
For tax purposes, a Single-Member LLC can be treated as a disregarded entity (i.e. similar to a sole proprietorship - all the business income and expenses go on your personal return).
Disclaimer: I work there.