OK, I have both those Celtic decks, so I'll try to de-enabling you. No promises, though!
Celtic Wisdom is difficult because while every card is connected to a myth, it's just one bit of the myth, and the whole stories aren't there. For instance, in the Mythic Tarot a whole mythological story is told in each of the 4 minor suits. That makes it a lot easier to learn and work with. It's very fragmented in the CW, on that level. Also, she has changed the names of not only all the suits, but also named the 1-10 cards in the suits with pretty clumsy and obscure names, so that it is very difficult to connect to the RWS numerical meanings that you may already know. It makes it very hard. The cards themselves are very thick, which I kind of like, but many people don't. I really like the art. And, despite all that, I really like the deck. I think with a lot of dedicated study it would be a great deck, but without it...sigh. I don't trade it away because I keep hoping that I will eventually put the time and energy and work into it that it deserves.
Yep, it's one of those.
The Llewellyn is a lovely deck, in every way, and the book is terrific for the stories. The symbolism is RWS, so you can just pick it up and read, without any of the mythological knowledge in the book. I'm not doing too well on de-enabling on this one...my own copy is still very new and fascinating to me.
I suspect it can be a deep deck--if I do the work involved. But in the end, I think for most of us, this deck will turn out to be just another pretty deck.