The Emthruster: Thrust without reaction?

[kch49er]

A recent study building on Forward's ideas is here
http://arxiv.org/ftp/arxiv/papers/1205/1205.2281.pdf
Ronan Keane and Wei-Ming Zhang have refined the beamed-core concept, so that it can achieve an effective exhaust speed of 0.69c, more than twice earlier estimates.
I think there would still be a significant problem with radiation (and waste heat) from such a system, but this is significantly better than previously thought.

does this affect the setting given that we have 0.25 as the amat clippers (unless these are an earlier verison\) presumbly faster amat ships would let further systems be colonised earlier.