marky_uk, In short, Syncthing is very suitable for Synology, also on Windows and Android. You have one alternative, but not the tools from Synology itself, because they are have always been unreliable with these mass of datas to be synchronized.
I will briefly tell you my story so that you know what I mean:
Since BTsync 1.0.128, mainly 1.4.111 I have been a productive user of this software, now with Resilio version 2.6.4. Resilio runs on 4 Synology servers, 5 Windows clients, 3 smartphones, 2 Tablets. The software is very reliable, constant observation was not necessary in the past. But the advances in Linux, Windows and Android mean new problems and bugs are coming up again and again. Unfortunately, the update cycle at Resilio is no longer practicable and very much to long.
Two simple examples with big consequences: The app keeps freezing on Android and in the meantime the Windows service cannot be installed in some cases on Windows builds >190x.
The first meant that I was forced to weave in Syncthing, which is possible with the right ignore patterns, so that the Android systems work smoothly - just embarrassing. One of the servers has now been completely switched to Syncthing and the coexistence of Resilio and Syncthing is working smoothly.
If the update cycles continue like now, I will have to change to Syncthing completely in the long run, since the administration is correspondingly more complex. In addition, Resilio wasted a lot of time and allowed Syncthing to become just as good and reliable, which was not always the case. It has also become more flexible in terms of features. The only real advantage of Resilio would be the selective synchronization, timely I use on Android, but currently I doesnt use. If Resilio allow Syncthing to completely overtake, it’s there own fault.
Finally the problems with permissions and so one are sometimes similar and I have to maintain in the same way. I am also a self-employed person and can understand that you need a quick solution, because all tests also require time and capacity. This laboratory work doesn’t help, I also found out. So in the end I just stopped syncthing on all devices, deleted all databases and started syncthing on all devices again. Since then everything has been going well. And dont forget regarding your Synology DS713+, Ignore permissions on “Yes” for each peer (folder) …