Build quality and materials. Those are the main differences. If this is your first genny, I'd grab a cheap close, just to make sure you like it. Then you can spend the money on a better one.
I picked up two did clones from a co-op and they have become my all day vapers. It took about two weeks of tinkering to get them to that state. Also, I've had a screw strip (the
threads, not the allen key part), and the air holes don't line up when fully tightened.
I will be dropping the money on a non-clone eventually, just need to get the disposable income for it.