Should I take the Accession Bonus?

I am an M1 who just did my Oath of Office for the 3 year HPSP AF scholarship! I was filling out paperwork and got to the point where I had to choose whether to accept or decline the $20k bonus (in exchange for 4 years of service instead of 3).

I'm currently considering either psychiatry (4 year) or one of the internal medicine sub-specialties (allergy, rheumatology, endo) (3 years plus fellowship). The issue is: I might change my mind!!! Whatever speciality I end up choosing, I just know it won't be surgery lol. And I'm not sure if I'll do a military fellowship. It's way too far out to even plan that ahead lol.

Should I take the bonus? My reasoning for NOT taking the bonus is it keeps things flexible in the event that I specialize in a shorter residency so I can just get in and get out if I don't enjoy being a military doc. I don't need the money; my family is more than capable of financially supporting me throughout my training.