The inside edge on blockers is simply that there really isn't a tremendously significant difference between most models.
Thickness of the actual blocker board, tapering of the nose (front/bottom) and the level of finger protection the goalie desires are among the different considerations to factor into making the right selection.
Most goalies opt to "match up" their blocker to their glove. This can be coordinated by manufacturer, size, style, or just the color scheme.
Recommendations
Senior ― 13 years and older
Intermediate ― 11 to 13 years old
Junior ― 8 to 11 years old
Youth ― 5 to 8 years old