I don't know how they stack up to credit karma since I've never used them, but personally every bank, credit card, etc. that I use seems to have their own credit score tool somewhere on their app/website.

I suspect they probably don't have quite as much data as something you're specifically paying for, they may update with different frequencies, etc. but if you just kind of want a good idea of what your credit score is and why, they're probably pretty adequate. Probably worth looking into whatever you already have before you look to throw more money at something.

Maybe nerd wallet but I'm sure they're owned by someone shady too.

You could keep using it and just ignore all the credit card ads they show you. That's how they make their money.

Just keep in mind, credit karma shows you Vantage scores not FICO scores. FICO scores are what lenders actually look at.