If you want to make a short comment about your own experiences, you can post them in the main 4.3.5 thread over here
viewtopic.php?f=151&t=143255#p683283
also if you encounter bugs, don't forget to post that to helpdesk
https://helpdesk.qnap.com/
So installed the QTS 4.3.5.0683 build 20180830 Public Beta ( 2018/08/30 )
https://www.qnap.com/qts/4.3.5/en
*update
QTS 4.3.5.0684 build 20180831 Public Beta
noticed a bunch of notifications, some of it is stuff like migration and fixing some errors during migration. anyway... wanted to start from scratch to avoid a patchwork of a migration that may or may not be doing things cleanly (no idea about that)
did a factory reset here (did backup previously of course. doing reset will wipe your data. so i don't recommend doing this without backups. also 4.3.5 is beta, so just do backups period

but that was not sufficient, and a reinitialization was required to truly wipe everything. so did reinitialization next.
the reinitialization was pretty straight forward, and when it finally completes, you then are greeted in QTS with some pop ups. You only deal with them once so no big deal. It at least tells you all the first things you ought to know anyway, then can close and make it not bother you again with the same message.
The most important first thing to do (cause you need to set it up and wait for it to complete raid syncing before actual use), is the storage manager setting up your volume/pools. That too was a rather easy process.
I created my first volume selecting the 4x4tb as thick vol raid5
there are resources online like this for example that will help you decide on your setup
From Youtube.com
but it felt that the sliders in QTS for setting up was quite sufficient for explaining your choices.
maybe it is also better to adjust the sync to take priority so that it gets done soonest. then later on i can change it back to medium setting.
in storage manager, usually by default the qnap suggests 50% utilization of your total usable space. i set aside 5% for snapshots (by going to snapshots and setting the reserve option). then after that, when i first created the pool/volume setup, i max allocated the rest for the pool/vol since i did actually need all of it.
the down side of doing this is, i cannot unallocate the space already allocated. so i need to be very certain about this allocation before i commit to it.
If later i need more space, i can unallocate the reserved space for snapshots and disable that feature. But if i get to that point, thats already a big warning sign that i would be better off adding another 4tb hdd and expand my storage. I got 2 bays extra for that, so i am future proofed for expanding my storage as my requirements may change later on.
Beta testing checklist - last updated, 4.9.2018
// just a checklist of things i've already tried and tested myself
1. myqnapcloud - works (also tested with lets encrypt https, and photo station service remote access. Also tested photo station sharing center to view shared gallery. everything working fine)
2. video station - works (also tested live transcoding with graphics card. also tested the media add on for front cover poster thumbnails. Though i'm not sure that graphics acceleration for transcoding is working fully)
3. photo station - works (facial media add on does not work properly ..

4. cloudlink - works
5. notification center - works
6. security counselor - works (a bug though with high risk yet report shows no mention of high risk item. misinformation bug?)
7. virtual station - works
8. storage manager - works
9 reinitialization - works
10. plex - works
11. qvpn - works (tested connecting to PIA VPN. To verify it works, i used download station and downloaded a magnet on an ipleak site to confirm the ip i get is from the vpn. I also tested from myqnapcloud to see that the registered device is also using the vpn ip. However have to ensure that ipv6 is disabled in the virtual switch settings to prevent ip leak. could not test qbelt because i only have 1 machine with qts 4.3.5 also the windows and android qbelt client app is not yet available)
12. virtual switch - works (however in overview, there was a temporary yellow/pink hue flash of the qnap model graphic when refresh on overview. Is a minor bug)
13. download station - works
14. hybrid backup sync - works (tested restore job from TS-653a and a TS-509 Pro to the TS-877)
15. snapshots - works
16. hd station (using hdplayer accessed via the remote RDP VNC. works, even tested plugging in aktimate mini speakers, and sound gets correctly outputted through them)
17. ssd profile tool - works
18. ssd over provisioning - works
19. scan hdd for bad blocks - works
20 - run smart test short and long - works
21. do network performance test - works ( https://github.com/adolfintel/speedtest and also with iperf )
22. qboost - i'm not sure that this is working properly. because i still had swap memory even after i ran optimize memory. had to reboot to fix my issue. i suspect qts 4.3.5 has memory leak issues somewhere.
23. qsirch - works
24. multimedia management - works kinda (but i'm not sure that the items being scanned shows proper number of items being processed correctly when you view from multimedia management UI in QTS. I'm also getting thumbnail generation errors every now and then during a scan. this seems to be an ongoing issue i've been experiencing)
25. update qts - works (however i may have noticed a louder fans or hdd noise not sure which, while it was updating from QTS 4.3.5.0683 to QTS 4.3.5.0684

26. test media playback with mpc-hc for windows 10 pc via samba - works
27. add login to win 10 credential manager and access to QNAP via samba - works
28. complete beta test program a - done
29. complete beta test program b - done
30. add third party repository in appcenter - works (even managed to install some apps that also are working such as onecd's autosort and nobanner in appcenter qpkgs)
31. app center - works (but i did notice the nvidia app in appcenter has a skull mark. removing it and installing nvidia driver app made that issue go away though)
32. spotlight - can't test this, i don't have a mac

33. report problems to helpdesk - done
34. locate nas - works (new music tunes working, also the led lights flashes correctly as well)
35. login with ssh winscp putty - works
36. resource monitor - works (temperature readings seem to be okay as well as far as i saw)
37. creating shares - works
38. encrypting shares - works (locking and unlocking encrypted shares works. Rebooting also auto locks shares, also works)
39. smart test and temperature scheduling set for all hdds - works
40. schedule and run raid scrubbing - works