Paying off rental mortgage

[Thomas Nagle]

I bought a duplex about a year ago and have about $81,000 left on the mortgage.  Paying about $270 a month to interest.  The place is prob worth about $130,000.  

I know a lot of people say it’s smarter to keep your money to invest into other properties but I was thinking of just paying this off and then getting a commercial line of credit on the place.  So I will reduce paying interest and can throw that money on the principal of my other properties. 
So I would still have the money sitting in a line of credit if I needed to put that down on another property and refinance the new property and pay back the line.

Any feedback would be great.