Pros
You may occasionally see some benefit from name recognition but frankly it isn't that significant as I have worked for local brokerages that didn't have a national name and clients didn't miss it in the least. This is the only pro I could come up with, and it isn't even a firm positive.
Cons
Just generic real estate, and they hobble new agents by taking too much split and trying to justify it by citing the training and marketing you receive, as well as... wait for it -- E&O insurance (pfft, please!). The marketing provided by the company is pathetic and will provide no discernible impact to the average agent's bottom line. None what so ever. The training is hit or miss depending on your broker within the franchise. This is the most important point - it is hard to review the entire company as the average realtor experience (especially newer agents in their first couple years in the industry) will depend on the particular office they settle into and the agent will sink or swim in accord with the quality of broker you hang your license with. I have been with one C21 that did nothing at all in terms of training, and I have worked for a different C21 brokerage that had fantastic training in sales techniques, contracts, etc. The numbers differential between the two brokerages put this difference in DEEP relief. The one with outstanding training is always amongst the top producing offices within the entire C21 system. The other office doesn't even exist anymore.