I've had that T.Lang DVD for several months. He has a wealth of knowledge. What is amazing is that you can tell this guy spent an infinite amount of hours breaking down, developing, practicing and perfecting his craft. What's more impressive is his ability to play anything with each limb independent of each other. When you talk about a drummer that has spent hours studying, you're talking about Thomas Lang. I still have not gone through that whole DVD. It's a double set with video instruction, pdf files and internet access to additional information. It is worth just watching, but if you need private lessons and can't afford to pay someone weekly or monthly, then this $50 value is well worth. He's got lessons to last you a lifetime. The question is are you committed to learning. Buy it and have fun.
Keep drumming.