The Eco button mainly just remaps the accelerator pedal forcibly turning a heavy right foot into a light right foot.
You can achieve the same result just being gentle with the accelerator pedal. I think it also reduces the maximum power of the heater however I can't say I've noticed much difference there and you could get a similar effect by turning the temperature down 1-2 degrees perhaps more effect.
It completely nerfs the feel of driving the car as it becomes a big heavy unresponsive lump and IMHO it can be a little dangerous if you get caught out needing a squirt of instant acceleration to clear a busy junction. You can get full acceleration in Eco mode if you push the pedal past the "detent" near the bottom but this causes a sudden surge of acceleration that is not easy to control which is not ideal. (The Eco mode bypass detent is intended mainly for motorway overtaking I suspect)
I can see use for the Eco mode as a "snow mode" as it makes the acceleration much more gentle and controllable for the same pedal depression, so if you find yourself in very low traction icy conditions trying to get moving, Eco mode will make it easier to do so.
It's also good if you have a passenger who doesn't like being chucked about as it forces you to drive very smoothly - many passengers don't like being chucked back and forth by the instant acceleration and regenerative braking of an EV, and it's sometimes difficult for the driver to realise how their driving style feels to the passengers.