TTL is basically your flash knowing what power to use depending on your light meter in your camera. Some remotes don't know how to send this information so the flash would be stuck in manual mode where you tell the flash how powerful to be. I would imagine most cameras and a decent flash on top of it would be able to use TTL. Some cheap flashes won't have TTL anyway, like my YN460, but my Canon 430EX does. However, when fired remotely with my cheap remotes, my 430EX loses the ability to work out the correct exposure itself.
I don't really know the difference between the two flashes Neil, but usually the bigger the number the better