[Gogar]

If you're the kind of guy who will buy the Ooni and then "what if" about the Karma forever then save yourself some brain treadmill and throw the extra $600 at it now because the $600 will be forgotten about soon enough. IMO

If you're a bang-buck guy and you will tweak the cheap Ooni to death and get amazing at it then you can look at it that way. Also a fine choice.

Or tweak it to death for $400 and if you get better than the oven - sell it for $400!