On my 12' x 44' layout, the majority of my curves I formed from Gargraves flex track. I cut curve forms from 5/8" plywood. I used string and pencil to create radii cuts at 48" (for O96), 44" (for O88), 40", 36", 32", 28", 24", 20", 16" (for O32). I measured the distance from center rail to outside of tie, then subtracted from the above radii when I marked the cuts, so that the O96 (and all the rest) would be center rail radii. As per Gargraves site video, you remove a couple ties at both ends of a section of flex track. I clamp ties against bending form at one end, then start bending from clamped end to the other end. I have not found a way to easily make a direct track to form match without a bunch on manual playing with the track. Once you are satisfied with the curve, you cut the ends. I normally have to use a lot of screws, some into the plywood below my soundboard, to hold the curve in shape. I am probably missing a couple things, but I think this gives you an idea. It takes me, a very novice person at bending track, 15 to 20 minutes per curve to get it bent and installed.
I also used scraps of plywood to create spacers that I can use to keep the distance between ties from an outer loop to an inner loop, thus keeping the nested loop spacing constant around the curve.
So you can see that, at least for me, there is a lot to do to use flex track.
So in my mind, flex track:
Pros - Cheaper, make custom esses as your layout requires, can make custom track to track spacing to give extra clearance between nested loops.
Cons - Takes a lot of time and patience. Use of screws into plywood substructure of you layout may increase operational noise.
