40 year note at 5% with no prepayment. Should I do it?

[Justin James]

I have the opportunity to purchase a Four-Plex for roughly $440,000. The units are all 2 bed 1.5 bath 1,000 sq ft. Rents are $850/unit with tenants paying all utilities except water, which totals approx. $300/month. Taxes are about $2300/year and insurance about $800. 

The seller wants to do/is offering seller financing as follows: $40,000 down with a 40 year term at 5%, with no prepayment. The note would be assignable. 

It is the no prepayment that gives me some pause, but I am planning on pulling the trigger.  This would be my first seller financing deal, but my 7th-10th doors.  Anyone have words of encouragement/discouragement?