It might be tempting to think of any mouthguard as a good option for dealing with bruxism. It would be a mistake to do so.
A night guard is not the same as a mouth guard. Yes, both appliances fit over your teeth. However, they aren't intended for the same purpose. Your custom-made night guard fits perfectly over your teeth to cushion areas that are most likely to be affected by your unconscious habit of clenching or grinding. A standard mouth guard is designed to reduce the force of impact from a blow to the face. Your custom-made night guard is made to protect your teeth from the vertical up-and-down force that's exerted when you clench and grind.
In addition to being made for the right kind of force, your night guard is also made to be comfortable for sleeping. A mouthguard that's worn during sports is thicker and bulkier in your mouth. This form could interrupt normal saliva flow. This may sound like a minor inconvenience that leaves you feeling parched, but there's more to it than that. While you sleep, saliva flows over your teeth to defend against plaque and tartar formation. Saliva also inhibits the activity of harmful oral bacteria. So, wearing a proper night guard, you not only feel more comfortable, but you can breathe more easily and enjoy all of the natural protections you'd have without your appliance.