Ventajas
There is a lot of tax education available to keep employees knowledgeable. They are slowing empowering their managers to actually manage. If you move, there are H&R Blocks everywhere. If you have the ability to continually re-adapt and adjust your personality to match your clients you will build a good client base (which is an expectation). You could make an okay income if you know how to do a complex tax return and you are incredibly proficient with their software.
Desventajas
There is very little room for advancement. They often impose unrealistic expectations for what they pay. The people who are creating the processes and making the rules have no idea what it is actually like to work in a tax office. They don't know when to leave well enough alone and continually change things that work. In 13 year with this company I had 8 different Managers. Lastly, It is very difficult to only work 4 months a year and earn a living.