It's not always easy. If I need to quickly move to the arrow keys (I touch type, so no looking!), I have about 80-85% success finding the right key on the first press... with the inverted-T layout, that's about 99%.

There's something weird about the way my brain handles the key being the same size as the option key next to it, and the fact that the tops of all those keys are exactly the same.

When you're searching for the arrow keys, the break is one thin line only in the middle of one key. When the keys are half height, there is are two large gaps to find. The difference is a few mm vs almost a cm and 3 targets to find vs one.