"Does that means that if i bought some from mouser and if i use arduino 12 bootloader and try to burn it, it won't work?"
I believe that is a true statement. Takes modification of the IDE to utilize the larger memories of the 328. Version 13 is suppose to include 328 support built in. Not sure of the bootloader differences, you will have to get some of the software wizards around here to 'splain all the gory details. In the meantime the Fundemental offering works fine if you don't mind using version 11 IDE for a few more days.
Lefty