Mike Fedora once said to me "You never see an olympic shooter shooting a flemish string, do you?"
I'd have had to reply "No, but I've never seen an Olympic shooter competeing with a Fedora bow either."
In his warranty he had (has?)a statement about flemish strings being less accurate, and possibly dangerous. I e-mailed him asking what this was based on, no answer. Saw some other crazy claims about strings by a different guy associated with different bow, couldn't get any answers there either. And the infamous "the flemish string (I) included with your bow caused the limbs to twist"--that was by far the most hilarious statement I've seen.
Endless strings are easier to reproduce one to the next, whether it's the same maker or a different one. Flemish have a lot more of the personality of the maker in them. Endless may add a tad bit of performance due to reduced string weight vs a flemish with the same strand count. I believe those are the two "biggies" with Olympic shooters. They use a whole different type rig than most of us, and they generally shoot much lighter weights and much higher strand counts. Just a different ballgame.
Flemish are more adjustable, and usually quieter (naked string).
Get down to it, either one works just fine if it's made right. You aren't missing anything of note with one or the other.
It just irks me to see misinformation purported about strings, especially by folks you trust to know what they are talking about.