It's all totally dependent on the Owner
Pros
SO MUCH INCREDIBLY HELPFUL support. I appreciated the crap out of it when I was there, but since I've left I miss it desperately. You can call and ask them any question at all and they will immediately have an answer, and kindly. No rummaging through 4 year old reddit threads looking for solutions. Just fast, compassionate, brilliant answers to every work question you could ever have. God I miss it. Lots of variety in the work, the workflow is easy to understand if your location is using the corporate software correctly. It's steady, reliable work, and if you can be organized and efficient, you can coast here for decades if you want to. The speed may seem stressful, and it can be real. But if you have a good owner with some perspective, they'll sometimes say things like "Listen, nobody dies if this isn't done by EOB today. We make signs not pacemakers. Their request was insane."
Cons
Your day-to-day is entirely dependent on the owner of the location. I had two very different, but excellent ones in Dublin, Ohio. An awful owner is going to be crippling, so pay close attention when you're interviewing. Speed is the name of the game. You'll get good at it, most Fastsigns aren't doing serious rocket-surgery design work. But the emphasis is do an upper-medium job, stupid fast. If it can't be upper medium, legible Helvetica crap will do. Every customer on the planet will say "what is this SLOW signs?!?" and you'll quietly barf in the background. Not a ton of room for growth, just because most of them employ 1-2 designers.