When I don't have the tank or stickybomb launcher (don't know which), the C4 explosion is just a light emiter that grows for the duration of the explosion. It still does damage. But based on what everyone is talking about, the explosion is really really small. Placing it directly on a window brick won't fakekill the window brick. At best you can use it to breach a wall of 1x2 bricks.
And as mentioned before, it only places in a set position. So often times it ends up sticking sideways out of the wall.
I think the model is ok. I would have personally taken that donated model, but its still decent.