Vantaggi
You will receive some experience preparing taxes. You will pay for your training and you'll pay, again out of your own pocket, for any IRS required certifications. The amount of aggravation that you'll go through will more than outweigh any benefit. You can get tax experience as an IRS/VITA volunteer.
Svantaggi
It would take probably an hour or more to list them all. I'll give the basics: lousy pay, lousy management, a generally poor and cavalier attitude toward employees. The pay starts at $9/hour. Apparently it's been at this level for years. Most of the management people are an embarrassment. My manager looked like a homeless person and I dreaded having to let her interact with my customers. Some of your fellow employees are ok; some of them are awful. The worst ones are the ones who have worked with HRB for years, although not that many people stay that long. Most preparers are gone after 2 or 3 seasons, when they realize that the job is far more trouble than it's worth. Oh, and don't get caught up in that "bonus" malarkey that HRB people love to talk about. A typical bonus is in the low triple digits. I spent 2 years there. Then I studied and passed the IRS Enrolled Agent exam and now I work for myself. My coworkers and managers never will take the EA exam because they know they're too dumb to pass it.