I've watched the Lenormand 101 videos and read the pdf's, and I have to say I really like what Melissa has done, and I thought she did a great job.
I do have some familiarity with the Treppner course. Four years ago I bought the course and worked with it for a while. I haven't looked at it since then, though, and I don't have it with me now, so I'm only going on memory. I liked the Treppner course, but I found in some ways it was too much information, at times without enough guidance (or at least that was my perception) on how it all fit together. For example, several different reading spreads or methods were presented but with no advice on what the big picture was; for example, how to choose between the different methods or in what situations one might be more appropriate than another.
In comparing the two, I would say that the Treppner course is, of course, completely text-based -- so there's large chunks of text that must be read and digested. The writing style is friendly but professional. It's geared toward those who want an in-depth textbook for the traditional methods (or at least one particular tradition).
Melissa's course is geared more towards people who have have little or no experience with the Lenormand, or who have tried but haven't quite been able to wrap their minds around it (I fall into that latter camp). Melissa's tone is much warmer and more personal, with lots of humor.
So I'd say the biggest difference is the scope. The scope of the Treppner is wider, with more spreads and techniques, if I'm remembering correctly. Melissa's scope is more narrow. There is some discussion of other spreads, but the majority of the course focuses on card meanings, combining cards, and the Grand Tableau. The video covering the GT is 43 minutes long, and Melissa goes into great detail, taking you through it step by step and demonstrating many different GT-related factors and techniques. I found it extremely helpful to be able to watch what's going on and to hear Melissa interpreting lines on the spot, as it were. The pdf which covers the Grand Tableau does go further in presenting new ideas on reading techniques, but at 21 pages it's not overwhelming.
I think Melissa's goal is to get people up and running with the Lenormand in as short and painless a manner as possible. This approach certainly works with me. I do feel that I have a firmer grasp of it and can't wait to start in on readings.
So, between the Treppner and Melissa's, I would certainly say that doing both would be great (although I agree with Astraea that it would be best to not do them both at once!). If you need to choose one, then I think it depends both on what your goals are and what kind of learning style suits you best. If you want a really comprehensive, all-encompassing course, with big chunks of text and a left-brain, analytical approach, then you might prefer the Treppner. If you'd prefer a more personal touch, with the focus on getting you reading with the cards and getting a good grasp on the GT as soon as possible, then I think Melissa's would be your best bet.