I want to increase my memory for a camera, and video camera that use SD cards. You have SanDisk 8GB memory card, model SDSDQ-8192-BULK, that is micro SDHC class 2 with adapter, and you have Centon 8GB micro SD memory card, model 8gbrsdhc, that is mocro SD class 6 with adapter. How do I know which is compatible? Also, what does BULK mean in the model number?