There is no definitive answer, because it can carry both pros and cons. I'm an AC in the Guard and a 6 yr regional FO. Overall, I'm glad I did it.

Pros:
- you will become a better pilot because of the amount of experience you will get operating in the 121 environment.

- the job is very compatable with flying in the reserves.

- your seniority and longevity is protected while on mil leave.

- with a draw down in military spending, it is nice to have the ability to go back to the airline to get a paycheck. The opportunity to bum is not there at my unit for the short term future.

- free ATP

Cons:

- the lack of pay and QOL for the first couple of years.

- You might be in the right seat for 5-7 yrs.
the so called pilot shortage will manifest as a " regional FO" shortage for the next 3-5 yrs. Hiring for the Good jobs will always be competitive. In order for you to get that quick upgrade, you either need attrition or growth. Regional growth has reached maturation. Regional 50 seaters will be replaced by " large RJs" allowing airlines to fly more seats with fewer aircraft. At most of the regionals, there are a significant number of " lifers" that will never leave or can't leave. If those guys don't leave or the airline doesn't grow, you will be in the right seat for a good while.

- the desire to get turbine PIC
More than likely, you will upgrade to AC before you upgrade to CA at a regional. I've spent 4 of 6 yrs on mil leave deploying trying to get PIC so I will be ready when the hiring starts. I'm concerned how it is going to look when I go to an interview and they start to take a closer look. Don't think for a minute that the HR folks aren't sensitive about it.

- higher potential for check ride bust, FAA violations and company discipline. Flying in the Reserves only, protects you from this. Ive seen CAs at my airline receive company discipline for refusing to fly an aircraft they thought was unairworthy, even though MX signed it off.


Some other considerations....
- I would not commute long term to a regional job, initially you may have to because you are junior.
- try to get your reserve job and your airline in the same city to improve your QOL