How effective are electric bug zappers?

Electric bug zapper mosquito killer bug fly insect attractant trap with UV light pest catcher lamp Portable standing or hanging for indoors and outdoors

Bug Zapper & Attractant 2-in-1 Mosquito Killer Lamp , 365 nm ultraviolet LED light attracts insects into the device, powerful grids kill insects instantly. Safety design + physical mosquito repellent, safety without radiation, non-toxic, free of chemicals, environmentally friendly and healthy for babies and pregnant women.

Properties:
Effective
Mosquito repellent --- Advanced 365 nm ultraviolet LED light that draws insects into the device and then captures and kills them via the high-voltage metal charging grid.
Security and Reliability --- Physical mosquito protection technology + safety cover with a gap of less than 7.55 mm. No radiation, non-toxic, chemical free, touch safe, environmentally friendly and healthy for family use.
360¡ã large work area --- The insect killing lamp is ideal for indoor and outdoor use. 360¡ã UV light provides coverage of 20-50 square meters. Place the device on a flat surface or hang it up anywhere with a practical ring. The power cord offers extended placement options.
Long lasting and easy cleaning --- The mosquito light killer collects insect residues on the bottom of the tray, which can be easily removed for cleaning, and the clean brush is included! ABS material durable and flexible, oil and wear-resistant, non-flammable, long-lasting.
Safety operation Wide range of applications --- Very quiet working mode, good for night use and without sleep disturbances. Perfect for indoor and outdoor use, as a barbecue party, kitchen, bedroom, etc.

Specification:
Plug: EU / US / UK (optional)
Color: Black
Power: 4W
Input: 100-240 V, 50-60 Hz
Suitable for indoor and outdoor use
Applicable area: 20-50 square meters
Item size: 282 * 137 * 137mm / 11.1 * 5.4 * 5.4in
Item weight: 560 g