It's pretty safe. You have to choose to send your info, and I assume
it's using similar technology to AirDrop, which you could already use to
share your contact info. The big difference is if you hold your phone
near another phone/watch, it gives you the option to do so easily.
The biggest risk is that there might be some NFC exploit, but your
iPhone will be using NFC anyway.
And FWIW, I recall Samsung having a similar feature about a decade ago.
Don't remember if it was an Android thing or a Samsung thing, but it was
neat, the few times I could convince anyone else to try it with me.