I'm a long time (many years) Synk user and owner of a 5.2.3 license that I use all the time. Last week I bought 6.3 as well. It has a very nice interface and some great new features I like.

Unfortunately, even though I've only been using it for a week, I've had to revert to 5.2.3 for my use due to speed and reliability problems. The speed issue is simply that a null synchronize (one where everything is already up to date) of several thousand files of about 6 Gb total size between my laptop and my desktop is noticeably (i.e. at least two times) faster in 5.2.3 than 6.3. I have no idea why, and I don't have time to experiment. As far as I know, I have the settings set identically.

But worse, after using 6.3 the sixth time or so, it came up the next time with a message saying something about the Synk preferences being corrupted and that it would move them and make new ones. I knew why they were corrupted, since 6.3 crashed on the previous run (which is in itself worrisome), but I didn't worry about it since I figured it would make new prefs and I could start over.

But instead, when it made the new prefs, it went into a a never-ending wait state where the window was only half drawn, and eventually I had to force quit Synk 6.3 to continue working. After retrying a couple of tries I gave up, removed all Synk files and reinstalled 5.2.3, which is working just fine for me now.

In case you're thinking the obvious, there is nothing at all wrong with this machine and it's working reliably in every way. (Trust me, I work on it 10 hours a day, every day, including Parallels and SheepShaver runs, so it's solid.)

So unfortunately I can't continue using 6.3 even though I now own one. I just can't afford the risk of unreliable backups. Synk is a wonderful product, but this version doesn't work well for me, and I'm permanently reverting to the very reliable 5.2.3. Your mileage may of course vary.