It is not illegal to have an exhaust cutout on your vehicle but it is illegal to use the exhaust cutout when on public roadways or highways.
In some states having an exhaust cutout on your vehicle could cause you to fail inspection.
Exhaust cutouts go between the engine headers and the muffler before the muffler.
Some people install the exhaust cutouts right after the catalytic converter before the muffler for the best sound.
Exhaust cutouts tend to last 2 years although they may only last 6 months to a year or even sometimes longer.
Exhaust cutouts are illegal in all states because they make the car louder and are a nuisance and driving down the highway or public road even in town can get you a ticket.
Exhaust cutouts do add horsepower as the exhaust is sent out the pipe before the muffler so it's not restricted by the muffler.
The muffler can decrease horsepower by restricting the exhaust and the exhaust cutout bypasses the muffler and increases horsepower but it also results in a noisy exhaust system.
Exhaust cutout valves are illegal and can get you a ticket when used in town or on the highway.
You can legally use an exhaust cutout such as on back roads, drag strips etc but on public roads, highways the exhaust cutout valves are illegal.
Having an exhaust cutout valve on your vehicle during inspection can also cause you to fail the vehicle inspection.
An exhaust cut out sends the exhaust out of a pipe before it reaches the muffler.
Normally the exhaust is flowing through the muffler which quiets the vehicle down.
But an exhaust cut out is an opening between the muffler and headers and when opened it sends the exhaust out through that under the vehicle instead of through the muffler.
Exhaust cutouts are an opening in the exhaust system between the headers and mufflers.
An exhaust cutout does help performance and increase horsepower although it results in a nosy vehicle and can get you a ticket in some places.
Clearing out the exhaust more quickly does impart more horsepower.
But, don't forget, bypassing the muffler makes for a noisy vehicle.
Every motor vehicle with an internal combustion engine shall be equipped with an exhaust muffler system in good working order and in constant operation to prevent excessive or unusual noise, and no person may use a muffler cutout, bypass, or similar device on a motor vehicle on a highway.
If you are currently running a stock system, you actually only need one cut-out installed before the muffler.
The life span is quality dependent, read your reviews and get a good one.
I have seen them last 6 months and over 2 years personally.