E3 is an ASIC, you can't use the Claymore miner with it. It already has the miner software included in the firmware. Claymore is only for Windows and Linux users. Even though E3 operating system is unix, it still won't work because its an ASIC and not a GPU.

If you get an E3 , you will need to flash the firmware first because they no longer can mine ETH due to the high DAG. If you flash it you can get a few more months out of it and then once it gets closer to the 4GB limit, you will be out of luck.

So if its cheap enough, get it. However keep in mind that its days are numbered for mining ETH.