Multiple connections can cause flue gases and sparks to pass from one flue opening to another, reducing efficiency and igniting unburned gases in the flue. They are efficient and easy to install, but should be UL-listed. Insulated factory-built chimneys minimize soot and creosote buildup because the inner walls warm rapidly. Both are safe and durable if constructed properly and well maintained. It is important to have an insulated chimney, particularly with an airtight wood stove.
Interior chimneys are preferable to exterior because they are warmer.
Also, round liners are more efficient than rectangular ones. Appearance and price are other considerations. Smoke pipe was never meant to be used outside. Water and ash form lye that quickly eats away single wall pipe. Also, creosote forms rapidly due to cooling of gases inside the pipe itself.