It takes a while to get your brain around the concepts of Formal Logic and Argumentation Analysis. If you feel like you're having that hard of a time understanding the principles of arguments, how they're formed, and why some are valid/invalid after a month in TestMasters, law school might not be right for you.
If, on the other hand, you "get" the arguments and the methodology but you are working full-time or have 3 kids etc... and just cant get your homework done, then yes, maybe it is a good idea to take it twice.
I'm in it now, too, and I have ample time to get my homework done, so I would never take it over because I would assume that if I didn't "get it" the first time around (over 2.5 months) then I'd be hopeless in law school understanding the concepts awaiting me there.
Im in a TM course right now, and it's going alright I guess, but I am still having a hard time grasping some of the concepts. The farther along I go in the course, the more I start to doubt being able to do well on the Oct. LSAT. At this point, I am seriously considering rescheduling for the Dec LSAT, and re-taking TM (in autumn) after I finish the summer course. Has anyone here ever retaken the course??? Did it help much??