The fundamental difference is how the drainage system is constructed. NDS EZ-Drain 4": This is a preassembled French-drain system. It contains a 4" slotted corrugated pipe surrounded by engineered Poly-Rock aggregate and enclosed in geotextile fabric. You install the complete assembly without separately purchasing and placing gravel. Dr. Drainage 4" corrugated French drain: If you're referring to their conventional 4" corrugated system, it uses corrugated perforated pipe with surrounding drainage stone/gravel. The stone provides the void space around the pipe and is installed separately.