I have a Guten, so I can only speak from my own experience but the quality is great for the price. I debated for a while over Guten / Brewzilla but in the end the thing which won me over was that with the Guten, the steps don't start until the unit reaches temps. With the Brewzilla, the steps start counting down the moment it starts heating. So for example
Guten:
Strike Temp - 70
Mash Temp - 66 @60m
Heating phase to next step - ?? but doesn't matter
Mash Out - 76 @10m (will only start once it's hit temp)
etc
Robobrew:
Mash Temp - 66 @60m
Heating phase to next step - ?? (Need to use a calculator to work out ambient temps, heating power, altitude, phase of the moon to predict how long to go from 66 to Mash Out temp)
Mash Out - 76 @10m but it needs to be set to 10m+previous calculation, maybe 21m or what ever
This is annoying, and pretty unintuitive. It means I can have a couple of recipes saved on the Guten, including Low, Med and Full mash profiles, a Hockhurz mash, etc (I think up to 9 recipes) and it will just jump per step without me having to do anything.
Other than that difference, they both make fantastic beers. I am not sure about the Brewzilla but the Guten comes with a 3 year warranty. That's a fairly long time. And if you consider the price point, you can afford 2 Gutens over 6 years for 1 GF!
Then again, sometimes it's nice to have nice things. I have become a believer in 'buy once cry once' and rather spend a little more for a good product, vs buying 7 Ozito Drills that I could have just bought a single Milwaukee (example)
However, there does come a point of diminishing returns, where you're paying more for not much more. At 3 year warranty, and almost a clone of the GF, both the Gutens and Brewzilla's make great beer.