Keep in mind you are comparing an AF camera that diverts some of the viewfinder light to the af sensor to an F2.
Most af cameras aren't ideal for manual focussing due to this.
I have an EC-B also but haven't gotten around to installing it.
The EOS 3 is a bit boxy/squareish shaped and the 1n is smaller without a BP or PB installed.
The prism on the 3 may be bulkier also because of the eye control.