I finally tested the new locking mechanism yesterday and I found it was easy to use and worked well. Even though I only lock the top slots and the old method worked for me, this method isn't difficult at all and works for players who lock other slots. Click the lock, select the slots, click the lock. Very easy. Note that I'm not saying there might not be a better method.
As far as the icons, I see them fine. Might be my monitor or graphics/UI settings or something. But I see it fine. I'm sure it will be easy for a mod to change that icon or even just change the tint color for the icon to make it more visible for those who need or want that.