One major problem with it, speaking as a 30-year old, is that it's not trivial to come up with some "ultimage goal" or "prime principle" for life. But maybe that's just me being unimaginative and isn't necessarily a flaw of the philosophy itself.
The real issue is that being consequent about stoicism seems to always result in contradiction given mankind's current state of knowledge. On one hand stoicism is concerned with not wasting time (on indulgences) and at the same time it ignores that a market economy (embedded in a democratic society) is the only way we know of, that can reliably force a larger population to strive for efficiency.
Of course the market economy isn't free - we pay for it by e.g. giving up moral values. It still allows for huge bubbles of inefficiency to form - things like complicance regulations that provide zero real value and only serve as market barriers. And of course we're all just fallible selfish humans, so there's no shortage of people studying and abusing these processes. But all these points are, practically speaking, irrelevant, seeing as how there are no (better) alternatives (yet).
So what is a stoic to do? Give up on a proven path to efficiency because he doesn't want to be a "tool"?
Just imagine how much more of our time would be wasted if there weren't an army of "tools" out there, working 8 hours a day towards the "indulgence" of ensuring that there is allways enough fresh milk stocked in the supermarkets of our cities.