I've run flex-fans on a few cars, all with good success. I've read the horror stories, but never had an issue nor ever met anyone who had one come apart. My current setup is a summit 7-blade flex fan and a homemade aluminum shroud on a summit radiator. Water pump and housing are 440-source units, and I run a 160 stat. My car stays nice & cool on the street, and is generally plenty cooled down by the time I get back to the pits after a run.

Just last year my buddies chevelle started getting real hot between runs at the track one day. We thrashed between rounds to find that electric water pump relay had crapped out. We had to bypass it. Turned out okay , but he almost missed a call. I know the OP is about fans, not pumps, but my point is I like simple & reliable.