I think one of the main differences is the quality of the connector supplied between the fixture wire tail and the main power wire you lay out from the fixtures to the transformer. If you get cheaper fixtures, this connector will not be water tight, and will eventually corrode and fail. For my cheaper fixtures I'm cutting the connector off and using direct bury rated (silicone filed) wire nuts, available at your local sprinkler store. I use the factory connector to lay the lights out and make sure I like there positioning and then go back and cut the wire and splice it back together with the wire nuts after I'm happy with everything.