I want to share my experience about the IGH.
There is a difference in the action of shifting gear between an IGH (internal gear hub) and a rear derailleur.
On a rear derailleur, when shifting gear, you need to keep on pedalling to engage the next gear. It is more difficult to shift gear when it is under stress, such as going uphill. And you cannot change gear when your bike is stationary.
Meanwhile, on an IGH, when shifting, you need to cease pedalling a moment to let the gear engage. You can even change gear when the bike is stationary. However, the gear won’t engage if you keep on pedalling and shifting at the same time. It is like driving with a manual shift stick where you need to depress the clutch to shift gear.
This is what I discovered after cycling on the Dahon Curve D3 with 3-speed IGH at Botanical Park Shah Alam.