I see the Octo 4 is a $130 cheaper.
I guess it would depend on having a cord in the water vs. none, or how important that is to you.
Myself, I like my Vortechs.
My current ones are 4 years old and I did have to replace 2 wetsides.
One when the magnet started to swell ( replaced it before it broke the plastic) and the one I replaced it with, the prop broke.