I would like to use a "safe dns service" like OpenDNS, SafeDNS or Comodo Secure DNS. I am in the United States.
they state for the best service is to add their ip addresses to my router. Usually they come with some kind of dashboard. If the service is in the router, how will the dashboard work?
Dashboard for the router or for the DNS service? You use the router dashboard to change your DNS settings to use the DNS services IP address, then, you use their dashboard to tweak the settings if you have an account. If you choose to use it without an account...
by using their ip's without an account, will I still get safe browsing against the porn sites and other similar sites?
Yes. You can use OpenDNS "Family Shield" to block adult sites by default.https://store.opendn.../familyshield/setup/
Don't know about the others.
For OpenDNS, I do recommend signing up for an account so you can tweak the controls for more fine-grained control. The only downside is that if your IP address changes frequently (dialup gives you a new address every time you connect; my cable internet IP address changes every 6 or 10 months, or when I have to reboot the modem) you'll need to manually check your IP address and update your account when it changes, or sign up for a service like DNS-O-Matic
to automatically update your account to your current IP.
I've been using OpenDNS for many years now, if you need help or have any questions I'd be glad to help out.