I used to be concerned about the Free Will versus Determinism issue. I'm not really that concerned anymore. Humans are not exactly controllable and observable in a systems theoretic with today's technology, and even if they were, the question still wouldn't be answered, because humans would still be doing the experiments.
Maybe we have to wait for the Robot Overlords to take over before we can get an answer.
Regardless, everything's densely interconnected.
Practicing mindfulness to achieve good behavior might not pay off every time like a slot machine, but it beats alternatives.
All that said, as long as you can make any kind of gesture purposefully, it appears that it is an absolute purposefulness, which can be forgiven as being taken as the appearance of freedom.
But it's not absolute in the sense that it can really stand apart from the 10,000 things.
But a lot of gestures equivalent to wiggling one's toe can add up after a while.
It's kind of like going to the gym: don't overdo it, but if you go regularly there will be results.
That probably didn't clear things up, so how about this: Whether or not we're purely meat machines or whether there's other metaphysics involved is outside the category of useful things that Buddhism discusses. (A useful thing that Buddhism might discuss is: I'm suffering! Must be an attachment somewhere! What's the way out? [Followed by a purposeful behavior.])