I have a GG/Curtis/Ross layout - no flex except a couple of short, odd segments; had a smaller GG flex track layout before this one.
Flex track: never again. Buy the pre-formed curves and make life simpler. The curves will look better in most cases. Save the flex track for stretches here and there where you need a little finessing, or a long, gentle easement.
Voice of experience. The difference in cost will fade quickly.