If you have an account with Fidelity, FZROX should be a better choice than VTI. Unless you enjoy investing or want to really get into it, either do a target date fund for the easiest and lowest risk, or a total market fund like VTI, or an S&P500 fund like VOO. You really don’t need to overcomplicate beyond that, except to potentially start buying bonds when you are nearing retirement if you didn’t choose a target date fund.
That is the downside, FZROX is only available to Fidelity customers. There’s also a potential risk it won’t track total market performance as well as predicted because one of the ways they keep the expense ratio at zero is by only purchasing what is supposed to be an equivalent subset of the total market to keep their transaction costs down. I don’t remember the specifics but I think they leave out lots of tiny companies and its not a significant risk because they couldn’t actually move the needle one way or the other.