Pros
Hundred year companies are unique - if they're single business line, it's easy to stay consistent as long as the product or service is accepted. In the same stretch of time if you've acquired , created and dissolved dozens of different lines of business there will be lots of good and bad experiences for every employee (and customer) ARMK's strength is its commitment to service, both to customer and community. As such, if dissatisfied in one end of the organization, there are a myriad number of other completely different business organizations, in lots of other countries, that are different and may have what you're looking for in a lifetime career. Overall, the company employee turn-over is relatively low, with company affiliation averaging somewhere between 7-10 years. Most with over 30 years, are not in management, so it is a place where if you're happy in your niche, or exploring the opportunities, odds are you will find something that suits you.
Cons
Being primarily in the B2B service sector, means the external market demands can be at odds with remaining competitive. Solutions here are often of the broadcast widely, and see which one sticks, methodology, so there can be shelved and ropped projects, experimental re-orgs, and many things that look good on paper, but impossible for anyone to figure out how to implement the results. Fortunately, the organization doesn't get fixated on plans that don't work - but that can be very frustrating or even depressing if you've spent a lot of effort towards something that doesn't pan out. And it isn't a place where you'll design and build rockets, but you will be providing polishing cloths to clean them, uniforms for the people who do that, and even serving food and drink to the very same people. Or supporting the myriad number of back office services that support them.