The word "benefit" does not apply here. The only "benefits" patients and families care about are: 1) does the patient live longer, and/or 2) does the quality of life improve in a meaningful way? Amyloid plaques are a surrogate marker, and (as already explained by many people in this thread) have not been established as a causal factor in disease. In fact, some work has even suggested a protective role for plaques. So we do not have enough evidence to say that a 42% reduction in amyloid-beta IN MICE relays any benefit at all to humans.

You are correct that a series of clinical trials, which would take 7-10 years, would clear things up. But for now, we simply don't know.