Flexible appliance connectors are listed for NG and LP. I agree Jon, that offset inside the shutoff box is a strain on that fitting. One good tug and you'll have a leak. Galv. with gas is an overrated problem. It is allowed now by both gas codes.

Unless a dryer or range, max. length is 36" per code. Those can have up to 6'.

HTH,
Bob

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Keep the fire in the fireplace.