Is a really with a dynamic IP address useful at all?
I’m running a node like that for over 5 years. Currently it is a guard too. The IP address is relatively stable and the major interruptions are due to kernel/tor upgrades or modem losing connection without the address change. Even after those it recovers pretty fast. Unless you are expecting to see downtime a few times a week, go ahead. The node is also useful even if it is not having the guard flag yet.
However, if you’re planning to run a node from your home, consider a few things. Forget about running an exit node: you will experience a heavy overblocking and hostility. And any node will bring some level of harassment, because ignorance is widespread. A second thing is that from time to time someone is trying to DoS nodes. In those 5 years I’ve seen a few of those, so I assume the average is like once per year of operation. Just accept the inevitable reality of running a node at home: there will be a day or a week in which you will observe thousands connections coming to your PC, all cores suddenly running at 100% without no apparent reason &c. Treat it as a way to gain experience.