Offset Pros:
Some of the best BBQ you will ever have
If you like to have control over your fire, you can't do much better than this, and you will do a lot of it.
Able to cook a lot at a time (depending on what size you buy that is).
Offset Cons:
They are expensive.
They take up a lot of room.
It is not a "set it and forget it" kind of smoker. You will be tending the fire and adding wood often.
Overall though, I would say it is still worth it. Don't go cheap if you go this route. Cheap smokers tend to leave you with temp and airflow problems.
All that said, I no longer have an offset because I like the ability to set it and forget it, especially for long/overnight cooks.