What are the main differences between Buddhism and Ellen Langer's 'scientific mindfulness'?
Do you have the passage? If you posted an excerpt it would be easier to answer the question.

But "scientific Buddhism", or Buddhist philosophy and practices adapted to fit a Western, secular audience, is not new. The Dhamma talks I've heard from teachers on retreat at places like the Insight Meditation Center in Massachusetts, focus much less on formal scripture and avoid metaphysics or the supernatural. Since the Buddha himself spent a lot of time de-emphasizing metaphysical questions, this is an easy step to take. Sam Harris has an entire book (Waking Up) that tries to convince skeptical, secular Westerners to practice Buddhist meditation.

On the plus side, this kind of approach cuts away the cultural baggage that grows up around any religious institution. Buddhism works perfectly well without spirits, devas, or reincarnation, and in this form it is easier for modern people to work with. Using the scientific method as a check on the woo-woo and wishful thinking that can corrupt spirituality is also a big benefit. (Does practice increase happiness? is a testable question, and it's reassuring that science seems to say "yes".)

On the minus side, emphasizing medical research showing that meditation and mindfulness are correlated with lower blood pressure, reduced stress, blah blah blah, risks taking a very thorough and rich spiritual tradition and turning it into a relaxation technique. Even people like Sam Harris, who take things like no-self seriously, throw out a lot of serious introspection in their attempt to strip things down.