I just brewed my second batch using his stovetop method and here's MY (keyword MY, not anyone else's) opinion.
AG brewing on the stovetop is a pain in the ass. It's produced my best beer yet, but it adds over an hour on to an already long process, and that hour involves work. Getting the grain and water into that pot sucks. It takes forever to stir up the grains. It's easy for water to overflow, or for wort to drip, and it just makes a mess overall. I have not had much luck maintaining a steady temp. It's difficult to take accurate hydrometer readings due to the suspended particles that slip through the bag.
That being said, most of that's due to me being a noob and not preparing and working out all the little bumps yet. I love his method for giving me the confidence to try AG brewing, but I will be constructing my own cooler mash tun ASAP, because I feel its worth it.
I have never experienced extract twang. I believe that as long as you sanitize, follow directions, and keep fermentation temp at proper range, barring acts of God, you will have a decent beer. The only batch I've ever had that sucked was due to my dad shutting the AC off each day without my knowledge.
If you're confident, go straight into AG. I do both, and use extract brews to experiment, and AG to make beers I know will kick ass.