I'm slightly concerned about routing my traffic through a non-major player in Anycast when I don't control the routing or software. I'd be worried it's quite an easy target for someone to do some DNS hijacking or packet sniffing.

There's a certain level of trust when I use 1.1.1.1 or 8.8.8.8. I'm unwilling to take the risk for this solution. I'm not sure what would help in the trust department to legitimize a solution like this.

This is why you should use their DNS-over-TLS or DNS-over-HTTPS service instead of standard DNS.

Route hijacks can happen to anyone, even Cloudflare or Google. If anything they're more likely to be targetted than a smaller player like Nextdns.

The difference is one has a dedicated security team and the other does not.