Depends probably on whether you value being able to see into the fermenter. I have a Fast Ferment that is translucent. While I can tell through it if the beer is clean or still murky if the light and my eyeballs are at the correct angle, I miss being able to see into it as I did with my smaller 5 liter glass jars that I fermented smaller brews in.
For sure it's a better price than the Stainless Steel conical fermenters isn't it? Maybe a AIO stainless might be had for the same. But I'm not big on AIO's. And then I absolutely would not be able to see my beer without opening the lid.
So what is of value to you? Long lasting would say get a $550 SS conical. But I can buy a few of the clear plastic conical's for that price and if I change how I want to brew and ferment, then I won't have a lot of lost investment. So that to me is more value.
I've had my Fast Ferment for several years now. It's not PET, but I think is HPDE, IIRC. I don't have to do anything special to clean it. Most everything comes of with a rinse. At most a wipe with a wet cloth. So nothing to really gouge the plastic. I'm fairly certain PET is similar. And will last long enough that I'll be satisfied with it's longevity.
I've been eyeballing that Fermzilla for a while too. Just need to convince the spouse that I'll die without it!