Ex2 ultra trying my first NAS to USB backup via dashboard - copy vs incremental

My Cloud OS 3 Personal & Network Attached Storage My Cloud EX2
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Did someone checked how copy/sync/incremental methods work?
Just got brand new ex2 ultra; running it on latest firmware 2.40.155. Need collective help to setup proper NAS to USB backup routine because WD manual and KS are not helpful.
I formatted external usb disk as ext4 and connected to ex2 ultra. Test folder with two files 123 and 456. Created my first test backup plan from NAS to USB with “COPY” selection. First run was 1:1. Then I changes content inside 123 at source and started the same backup again - at the target, in addition to 123 it created new file 123_1 with updated content - is it by design? KB has vague statement “Duplicate files will not be overwritten” which is ok but having files _1 _2 _3 etc is not ok.
Went to change backup method and saw that “INCREMENTAL” in available - is it bug or feature, because as per KB its not supported? Changed selection to “INCREMENTAL” and completed few more test backups. Looks like its working - it created new timestamped folder for each run, and each timestamped folder has correct content. Should I stick to Incremental, because all I need is a kinda safepoint type backup from my cloud gen1?
https://support-en.wd.com/app/answers/detail/a_id/20227