when are you planning to visit? I ask because I was planning to purchase through LMT but the ticket promotion DL is running now through the next couple of months ended up at basically the same price, even with Maxpass added. (I purchased 4 day park hoppers FYI)
I have used them multiple times with no problems at all, though as lsumatt mentioned, if you are going in the spring while the current promo is going on they won't give you the usual huge savings compared to buying directly from Disney (and if you use gift cards bought with a Target Red Card at a 5% discount you will actually pay less going through Disney). However that is only during this promo period.
Used them last summer and no issues and will use them again if they are the lowest price. Don't forget to search for a free membership so you don't have to pay.