If you are a buy & hold investor, the Land Contract doesn't mean much for you unless you were trying to then sell the property or obtaining additional financing with this property as collateral. The details are what matters, just as they would in any other deal. Are there prepayment penalties, is prepayment allowed, when are you granted possession, is the Vendor paying for title insurance on the front-end or are you responsible for it? One unique aspect of a Land Contract is, are you responsible to pay Vendor directly for property taxes & insurance, or are you responsible to pay property taxes & insurance directly? Vendor is able to call the balance immediately due (page 3 of the WI Land Contract form 11-2003) if you fail to pay as this page outlines.
To be honest, as long as you're holding up your end of the deal it's more of a risk to be a Vendor than a Purchaser in a Land Contract because they're assuming the risk that you run the property into the ground then have to take it back via foreclosure. In my opinion 20% down, 3.9% interest. 30-year AM with a 10-year balloon is a good setup for you for a 6-unit property, as commercial financing in my area is 20% down, 4% interest, 20-year AM with a 5-year balloon.
Were there any specific concerns you had about a Land Contract? I have been the Purchaser in a Land Contract for almost 6 years now and I worked on a fair amount of them with clients in a previous life so I know enough to be dangerous.