I have previously fermented in cornys (and am currently rebuilding my set up to do so again) and it’s brilliant. The only downside is that you can’t ferment a full batch at once. Im working around this by no-chilling and then fermenting 15L at a time.
I preferred a corny to the fermzilla for many reasons. It’s cheaper, it’s more robust, the keg can be repurposed back to a keg if you later decide you don’t like it but with a fermzilla you’re stuck with a fermzilla.
There is a product called a Kegmenter from KegLand which looks really good, but you have to buy an extra lid for it and it works out quite expensive compared to a corny. Here’s a link to a video with a bit more info:
One tip - rather than cutting the dip tube shorter on your corny, switch the beer tube for a gas tube, then put a floating dip tube on the end. It’s easier than hacking bits off your keg, and it filters the clear beer off the top of your fermenter rather than sucking up trub from the bottom. I use this one which is great as it has an inbuilt filter:
https://caskwidge.com/Parts/Product/17