How is a kosher restaurant open on shabbos (you pre-book meals) any different to a kosher hotel? or a frum caterer, catering a simcha (often all 3 meals + kiddush)?
Would you not buy from a kosher certified business <b>because</b> it has a hashgocha to be open on shabbos, or are there other issues?
I would assume this hashgocha (and any like it) caters to people & places that dont have any other kosher options, but it may not be acceptable to frum yidden, especially when there are other better options available.