Unless I am confused I think 1.06 is in beta test.
JW
The only change in FW v1.06 is the addition of support for FTP server passive port configuration. Keep in mind that FW v1.06 was released in 2012. I have two DNS-343, both of which are running FW v1.05 for 2.5 years (and counting) without issue. If you do decide to upgrade your FW, you do have the option to regress to an earlier version.
Please make sure you backup your data to another physical device before performing any critical updates/fixes. If your DNS-343 is configured in a RAID configuration, please keep in mind that RAID provides redundancy, but is NOT a backup.
I tested FW v1.06 on one DNS-343 for the purposes of offering support and subsequently moved back to FW v1.05, which I found to be more stable. Additionally, the changes to FW v1.06 did not provide any added value for my use case -- if it's not broken, then don't fix it! The "b" identifier after the firmware version number is short for "build", not "beta". That said, Firmware v1.05 is the version that has had the widest distribution and seems to be the most stable, it's also the first FW version supporting 2 TB AFD (advanced format) HDDs, which is critical if you're looking for a replacement 2TB HDD that's supported by the unit.