I bought my blade III 4.9 about 6 weeks ago with the bar option & the X over kit was already attatched to it. According to Flexifoil blurb it comes standard with the bar. And not a bad idea at all.
To the unwise the X over kit is a single line of shockcord running through the centre hole on the bar with a pulley on the end with an 18" length of cord running through the pulley to which the brake lines r attatched 2 each end, thus when the bar is pulled down to the left or right the exact amount of main line travel is X over in the brake line keeping the trailing edge on a same plane as the leading edge. I agree Lansdown a must, try & then buy.