I wouldn't start taking any tests yet until I'm mostly or totally done with content review. Maybe take one to diagnose your starting point, but that's it. I took 2 TPR tests early on in my content review, and let me tell you now, they were POINTLESS. They took time to do and they are completely useless now to me in terms of anything. Of course I missed a bunch of questions-- I hadn't reviewed the topics yet.
Actually, the course in general kind of was a waste because while the classes were helpful, the content didn't really sink in until I actually had the time to sit down myself and really learn the material. Right now after I've already done the content review myself, I think having a class to go to would be helpful. Kind of backwards I know... if I already have the content down, why go to class? But seriously, trying to "practice" by doing tests or practice passages before you've got the content down comfortably, is just kind of a waste of time. Yes, it teaches you test taking skills, and maybe it's good practice for a test situation where you have to learn how to make educated guesses based on the passage while not knowing the content. But, it's really not good for much else, because since you don't have the content down, as soon as you've done the passage you forget the material it tested. So, if you *are* taking a class, I would suggest really trying to review the content beforehand or at least keep up with the class as you're attending it. It'll have more of a lasting impact that way.
Anyway, that's kind of a digression
But, all that is just to say, don't worry about taking practice tests early on-- by the time you actually finish content review, and you look back on those earlier tests (if you took any), it'll be like they were written in a foreign language. The mistakes you made won't correlate at all to the stuff you know, and it will have just been a waste of time.
