That's a good point... Though the connection will be through the wall and inside to the black iron... I'm hesitant to put the hose inside the house as it wouldn't be as fire resistant... right?
I would go with the hose, that generator is going to vibrate, and the flex pipe will break.
Both may be an option. Piece of the CSST, then the hose externally. Would be able to buy a much shorter hose then. I've also got the break-away valve to figure into this, as well, if I want to.