Since v2.9-beta2-1-gfc1d1d0-alpha the Blip size slider doesn't work correctly. The Blip size slider should change the icon size inside the minimap, but it changes the size of the whole minimap instead, which makes the minimap look "weird".
Also the Opacity slider doesn't work either. At 0% the minimap disappears, and from 5% to 100% the opacity is always 100%.

Oh hell, I completely forgot about that.

The issue with the Opacity slider however only happens when you are indoors (f.i. class order hall). If you are outside (Dalaran Courtyard) it will work as expected. Sadly this is a Blizzard limitation and cannot be fixed.