I have both, just picked up the Zoia a couple of weeks ago.
My general feeling is that the ER-301 is deeper and has an easier to use/understand UI. Zoia is more tactile/hands-on and has better effects (especially when it comes to reverb).
They do feel similar in some ways. The patching process is very different though. After patching with Zoia, I’ve come to have a new appreciation for the ER-301’s signal flow. Working in chains/subchains, how everything flows from left to right.
Patching in Zoia is very much like actually patching in a real system. All the connections have to be made manually. It can be easy to lose track of what’s going on as you build more complicated patches, especially as you build a patch out across several pages. Because of this, easy access to every module’s input and output is available. Whereas on the 301, access is limited by using local controls in a unit, or global chains.
The tactility of Zoia is very fun. All of the buttons and stomp switches can be made to do almost whatever you want them to do. I recently built a dual looper where one button toggled the recording on both loopers, and another button reset both looper completely. There’s a keyboard module that allows you to customize the note each button outputs, as well as how many notes the entire keyboard takes up.
I still have a lot to explore with Zoia, but that’s been my initial findings. I’m glad to have both as I feel they work well together.