There are two main variations of the controllers, SD something and SH something (I will look it up later at home). They are very similar but have a shift in a pixel or two. The controllers are embedded in the glass,between the display and the flex cable. To know the operating voltage, check the datasheet of the controller and the schematic of PCB itself. Some like adafruit provide both an LDO and 3.3 <-> 5V level shifters, that's good. Other, claim to be 5V compatible but run the controller out spec, on the supply and/or the input pins. There are also different variations that look exactly the same but are different (different color, different controller, etc), with no model number and the seller don't always know what they sell It's quite messy when you buy from the Chinese sellers on ebay.
I get mine directly from Heltec so at least I know what to expect.
Hope it helps.