Mortgage Term/Amortization, is it worth it?

[Tyler D.]

I am looking to refinance $50k investment property and was offered a loan with 5 year term/25 year amortization. The rate is better than anything I can get with a normal loan (4% vs 5.5% for a 20yr fixed refi). 

As I understand it, my loan would be paid at a 25-year amortization rate and I would need to refinance it after 5 years. Does it make sense to do this, or am I better off taking a worse rate for a normal fixed-rate mortgage?