I have flashed five motherboards. Four worked a treat and i bricked one. There was a pattern though,the four good ones were quite moddern boards,farely new like and the one i bricked was an old one. But i do put it down to me getting too big for my boots. Always a risk but one worth taking in my opinion. Try the first one you do on your own motherboard.
In most cases flashing a Bios mod (made with the proper Method by an Experienced User) is as safe as flashing an unmodified Bios. There is always some risk. Always make sure you: 1. Have a Recovery Method ready Before you Flash. 2. Have the Correct Bios for your EXACT MB. (Physically Look at the Model # on the MB to be sure). 3. Flash from DOS (NOT, a DOS prompt in Windows) with the Correct Flash Utility for your MB. 4. Run the Unmodified Bios Version on your MB for a few days/weeks and make sure it works properly and is stable BEFORE you flash a modified Bios. 5. With a BIOS, Newer Version Does NOT always equal Better !!!! Ultimately, If you are not comfortable flashing your BIOS then use a Loader or Purchase a Key.
Some motherboards, like Asus, have a flash utility from the bios. Thats the best method if available. The Asus ones can read ntfs etc, you don't even need to put it on a flash drive! Keep a backup on a flash drive though of an unmodified bios. The safest thing to do is load default values for the bios then flash. You don't want to freeze your computer during the flash due to overclocking! Also don't do it at higher power loss risk times, like hotter weather as in 40C or more. Hot weather increases demand for power, which among other things can cause failure simply due to the load on transmission equipment coupled with the heat can overheat/overload (they have massive fuses that can blow). Also don't flash when there's thunderstorms about, fires about, flooding, or when its very windy! Night time is the best time to flash, when its not in the situation like above, as power is less likely to go off during the night! (its true)!