The Tai Chi in SD is literally Cheng Man Ching's 37 posture form (shotgunned in 2 places [hanging lotus/cloud hands]) and Chen Zheng Lei's 18 posture Chen form, for starters. The SD applications are generally pretty simple (from what I remember). Tai Chi is basically slow Longfist. I know that's a simplification, but if you've done Longfist for decades, you know this to be pretty true. The applications in SD's Tai Chi are elementary, and often unrealistic (take "single whip" as a backhand slap and then a palm push--lol--when in reality it's closer to the way SD teaches chin-na hip throws). Get what you can out of it, and definitely avoid the new age crap. But you can improve your form even with video instruction. I remember starting THERE--with video instruction to fix my form's mechanics. Luckily, I've crossed paths with many talented Tai Chi practitioners (traditional Yang, Chen, and Sangfeng Pai) whose lessons always pushed my mechanics even further. I have my own judgments about Cheng Man Ching's lineage--they almost all practice as if they too were midgets (the master was a tiny guy, so his own edits to the Yang long form tended to stress his natural advantages of a low center of gravity that doesn't require much movement to get lower); and they perform it as if they too were rather lacking in a certain "long-limbed" athleticism.
I also greatly enjoy Cheng Man Ching's book (13 treatises). The man was a scholar. His written instructions/reflections for practice can really hyper-focus your study for improvement. The man goes on for pages regarding the proper alignment of your wrists in the first motion of the form. LOL.