At first I disliked the idea of having two dashes, but the two dashes are each useful in their own way, so now I'm realizing that what I actually hate is having two dash buttons. It would make more sense to have a single button for the regular dash that would activate the shield dash if pressed while you were blocking. It would make much more sense than the current setup. In the very least, there should at least be a box at the bottom of the control menu you can check that says "hold block and dash to shield bash?".
Edit;
Please note that the shield dash activates IF you press the dash button WHILE you hold down the shield button.
You have to be holding down the shield button. Your shield actually being up or down is not what is required.
This means you can shield dash before your shield activates. So the shield raising delay isn't transferred onto the dash. It also means you can regular dash after releasing your shield button before your shield is lowered. So you can block and then dash away normally, without having to let your guard down for a small second in order to not accidentally do a shield dash instead.
Good idea.