I have both. As near as I can tell, they are the same deck except that the Pathfinder version is larger and the gilding is different. The Pathfinder's is 5.75 inches by 3.25 inches whereas the Truth-Seeker's is an inch shorter and about a half inch narrower. The backs of the cards are the same in both decks. The main difference I saw was in the gilding. Both decks have a lot of it, and in both the same items are gilded and in the same way. However, the Truth Seeker's gilding is very bright--mirror bright like gold foil--and the Pathfinder's is more subdued, almost matte, more like gold paint, I would say. As for the images on the cards, they are identical, as far as I can tell, down to the last pebble.
I bought the Truth Seeker's first along with its book as a set. I used the deck several times a week for about a year before moving on to a different one, but I kept the book around as a reference because it is based on numerology, mostly, instead of Waite and therefore gives you a slightly different point of view. Then I saw the Pathfinder on E-bay and bought that because I thought a slightly larger deck as a back-up would be nice.
Some time passed, and when I returned to the deck, I found myself using the Pathfinder's more often. Now I prefer it, but only slightly. I like the more subdued gilding and some of the shading is more obvious in the larger format--for the majors, anyway. I still use both, however. And the bright, foil-like gilding of the Truth Seeker's has held up to a year of steady use.
Hope this helps,
greycats
ETA: probably the reason Truth Seeker's is not so well liked is that the minors are only partially illustrated and the deck is not formatted like Rider-Waite-Smith. gc
