ECN-2 differs SIGNIFICANTLY from C-41.
ECN-2 starts with a prebath (chemical process Kodak PB-2) which physically removes rem-jet backing after the solution softens it. Either a spray or a physical scrubber are used.
The ECN-2 developer is specified as 3:00 (180 seconds) at 106°F (41.1°C). It uses Color Developing Agent 3 (CD-3).
Meanwhile C-41 uses a completely different developer (using CD-2) at 100°F (37.8°C) 3:15 (195 seconds).
As far as secondaries are concerned (bleach, fixer, stabilzer) there are differences, but C-41 and ECN-2 2ndaries are completely interchangeable, might be slight tweaks in the process commercially, but using one shot, and as they're all develop to completion, I'd just up the times 10% if flip-flopping, and they'll be perfectly fine archival negatives after that.
C-41 2ndaries are probably of a higher quality. They are definitely more expensive. ECN-2 2ndaries are cheaper, per unit volume, but tend to be available at a MINIMUM size of 100-L. This precludes the casual user from obtaining them unless they are friends with a motion picture lab.
One can also mix ECN-2 developer according to Kodak PDF instructinos, but even there the chemical list is lengthy and the components expensive.