I wouldn't use fantasitrade for exact values when making card to card trades.
You should trade based on what you need and want.
For me, I would consider Eriohnet, along with any other D speed mages, to be worth 0te as they are worthless to me for event I like to rank in. I would only trade for them if I really like the art and/or sprite of the unit.
You control what the value of a card is worth to you, not fantasitrade. That site is just good to give you a ballpark range of what you could get for it.