I didn't find the shape preview very useful.
The increased bomb damage might be a bit underpriced; at the time I purchased each level, the bombs were already destroying tiles completely.
The way the game counts up all the gems at the end of a run is a bit confusing; at first I thought it was giving me extra gems.
The upgrade that lets you see multiple layers is kind of weird; it would probably make more sense if it let you see X layers beneath the current top layer, instead of working in "blocks" of X layers.