Is this tool by NerdWallet reliable to calculate location wise COL?

No. There are no calculators on nerd wallet that are any good. That said, most CoL calculators look at 'mean" value of things, like housing. The "mean" house in Sunnyvale, CA is most likely much, much smaller than a house in a MCOL, so it's not just a pure numbers game. My house would easily be a multimillion dollar house in the bay area but a cost of living calculator isn't going to account for that, it just uses mean vs mean.

Even our comp team wouldn’t use them to adjust salaries 😂