It's impossible to do one perfect yoga vid. At one end of yoga there's full-on Ashtanga (which this isn't) and at the other there's moving your fingers around and going "Om". This one appears to have taken Ashtanga, toned it down a bit, and found a level that won't turn you into a perfect physical specimen, but will keep you in reasonable shape mentally and physically if you keep it up. Then they've got Penny in and marketed it at women. All good stuff.
This DVD won't give you muscle definition like Madonna or Sting. For that, I thoroughly recommend David Swenson's Ashtanga vid, which you can get from yoga specialist suppliers. It really goes into the whole Ashtanga thing in great detail and will take you from beginner to a very advanced level, muscles and all. But if you're the kind of woman the Penny Smith offering is aimed at, I'd hope you'd rather have a bod like Penny than Muscly Madge anyway!
The only criticisms I'd make of this DVD are:
1. It doesn't give you much of a path forward to improve. If you're like me you need more challenge all the time, and it's important that if you're going to do easier versions of poses (and most of them are in this DVD) you should know what version you're working up to.
2. One fundamental component of Ashtanga that's hardly mentioned at all here is "bandhas" or "locks". This is all about holding your abdominal muscles in a particular way right through the practice. Without it you'll lack focus, balance and strength. You'll also have a flabby tum.
On the up-side, Anton has included some great intermediate techniques that save us mortals from some of the most strenuous moves and positions, and Penny makes the whole thing very accessible and reassuring. This DVD's not much good to a complete beginner, but if you've done a few classes and want a DVD to do your stuff at home to keep everything pointing northwards, this'll do it. But once you're bored with it - go buy the Swenson one!