Is SonicWALL "WorkSet" firmware ok to load?

My client has an old SonicWALL TZ 210 with firmware 5.9.1.10

The latest firmwares from the MySonicWALL site are:

sw_tz-210_eng_5.9.1.12_WorkSet-5.9.1.12_4o_1178016.sigsw_tz-210_eng_5.9.1.11_WorkSet-5.9.1.11_3o_1167025.sigsw_tz-210__eng_5.9.1.10.sig

The 2 most recent files have "WorkSet" in the filename. They are categorized as "Maintenance Release".

What does "WorkSet" mean? Should a "WorkSet" firmware be used in a production environment? Is the most recent WorkSet OK to load onto their SonicWALL?

Thanks