I don't know what what diameter sausage you're looking to poach but those from normal hot dog size (22-26mm-ish) to polish sausage size (36-40mm-ish) will come to temperature in something like 20-30 minutes with the water only 10 degrees above your target internal temp.
I'm unsure of the reasoning behind a turkey roaster but without specific info suspect it's because that's the pot folks have that the sausage fits into (if the only tool you have is a hammer everything looks kind of like a nail). An electric roaster seems like it would be just about ideal. I'll have to try that.
As far as the stove top, my experience has been that a tall pot is easier to hit and maintain my target temp with than a short fat one is as sometimes a pot much wider than the burner has hotter and cooler areas and I wind up agitating the water to even them out. With either one though the fact that I can sneak up on the target temp and not worry about over cooking things means that I've become a big fan of poaching when it's appropriate.
In any case, a candy thermometer is a great aid to hitting and maintaining your target temperature. You can get an electronic one with a temperature alarm for $25 or less and an old school mercury bulb style one for $10 or so.