Good flared connections generally cure leaks or in some cases some teflon tape or LP compatible pipe dope may be needed.
Many users who encounter low flow issues are using too small of a cylinder to supply the demand. A 20# cylinder will not vaporize the liquid propane fast enough in cold weather to keep up to some furnace requirements, especially when something else is drawing at the same time, like the hot water tank or cook top range, etc. Using 30 or 40# cylinders usually will cure the problem.
Beyond that rambling answer, looking at the part from Camco, I don't see how you are going to cure your problem with it. The item you are looking for is an extend a stay fitting that installs between the on board tank and the on board regulator and allows connection of a separate cylinder to feed the system.
