I have a first gen My Cloud which I upgraded from a 2TB (failing) drive to a new 4TB WD red plus drive.
I reinstalled version 3 firmware which great help from Bennor. It’s like a new system!
I disabled cloud access as I only use this drive for my personal home network (file backup and media). Is there key benefit updating the firmware to V4? Everything I need this NAS to do is working and I hesitate to take a chance on something going wrong.
Read the v4.x firmware release notes files and decide for yourself if updating to v4.x is worth it. Generally its wise to update simply for the various patched security vulnerabilities and any services or module updates.
Personally never had a problem, that I can remember, updating from the Original_v03.04.01-230 firmware one can use to unbrick a first gen single bay My Cloud to the latest v4.x firmware in all the years I’ve messed around unbricking various hard drives on a first gen single bay My Cloud. YMMV and all that.