There are 3 types of Pa Kua (Bagua/Bagwa) Mirror - flat, concave & convex.
All types prevent the negativity from entering your home if correctly placed. They will correct Feng Shui predicaments by deflecting almost anything that creates Shar Chi (poison arrows/negative energy). Pa Kua mirrors should only be used outside the property. Hang above the front door wherever possible. Cleanse your mirror before hanging and on a regular basis by wiping with a clean damp cloth and passing through some incense smoke.
Flat - disperses negativity, concave (the mirror is curved inwards) draws it in & holds it; convex (the mirror is curved outwards) directs it back where it came from.
The most widely used is the flat type as it does not cause any harm. This type will provide good general protection for most properties.
The concave is used where it would be a problem dispersing negativity (e.g. very closely enclosed areas. Concave mirrors magnify a reflection when close and will turn it upside down when farther away. The act of turning a reflection upside down will also make it smaller. Therefore, a concave mirror is used when large objects point at the front door or home. They become smaller and pose less of a threat. For example – if you have a large tree in front of your door then you could place a concave pa kua mirror to reflect it and shrink its image. The concave mirror draws the negativity into the mirror - not the home. As the concave mirror draws the negativity in, it needs to be cleansed on a regular basis to ensure effectiveness. Cleanse by wiping with a damp cloth and pass through some incense smoke.
The convex needs to be used with extreme caution - I would never use opposite a residential property - no matter how bad the neighbours, as it could cause extreme bad health to afflict the residents. I tend only to recommend these to combat objects such as electricity pylons.
Feng Shui is not about harming others, so, I would choose a flat mirror in most cases, unless there is a specific object causing a problem.
For general street traffic use a flat one. For the side - it depends on layout & type of negativity.
If you have a door on the side then hang a pa kua mirror above it. If there is only a window then hang a Mayan Ball in the window. If there is neither, then no negativity will enter.
For indoor use, to disguise a toilet, bathroom etc., use a plain flat octagonal mirror with bevelled edge – not a Pa Kua mirror. This should be fixed to the outside of the door above the throat height of the tallest resident.