That makes secondary mode pretty useless. Good reason to change from 1H to sec mode 2H would be stabreach. but without this and 34c 25p it's the worst 2H ever.
I found the fighting axe to be a much better 1h/2h weapon. 1 slot, decent speed, decent damage, and bonus against shields.
As a 2h with shield skill, you can keep your shield out until you are on top of a ranged opponent; you can then switch to 2h mode to instantly put the shield on your back. If needed, you can switch back to 1h mode to instantly pull the shield out again.