Anybody have experience using those foam devices that keep your rods afloat if you capsize? Do they get in your way, or affect the line while casting or retrieving?

Can't say that I have ever confirmed they keep my rigs afloat but I use them.
I tape the ends with duct or electrical tape and that keeps them out of the way of your line.

I have a set but don’t like fishing with them attached. That’s just me.

I grabbed a set and have been using them in my kayak. I didn't like how much they moved with the velcro straps so I cinched them down really tight with zip ties. That keeps them more toward my reel and away from my eyelets. Once in a while during a cast, the line flies over and sticks to the foam but it's easy to flip back off and reel. Also sometimes during casting or reeling up slack you can hear the line who against it. I have tested them and they float my spinning setup, but my zebco 33max is too heavy and I'll have to leash it.

Overall I think they are easier to me with than a leash for sure and I'll deal with the minor inconvenience for the security they provide.