I prefer the Meinberg NTP implementation because it profiles how your clock is drifting so it can adjust it in real time with fewer trips to the internet. I am storing quotes and log files which have timestamps, so it is important that the clock doesn't jump around when it synchronizes. What was funny, when I was playing with this, I tried an app set to fix the clock every hour. In the test case it worked fine, only adjusting a few milliseconds every hour. But in real time it failed, because higher CPU causes the clock to drift much worse during the real trading day (I think this is only an issue on multi-core computers)
It is even more free for WIndows as you do not need a program. Windows itself syncs time. Regularly. At least modern versions. They stop on a 5 minute difference between their time source and the local clock as they THEN note something is really fishy