read the thread pal, few pics on here, it allows the isofix to be used and then the rear tether so it doesnt hold firm solid to the seat but if they're was an accident it would stop set lunge due to it now being rear tether mounted using the isofix bracket to create more security to the seat.. most use both..the belt and the bracket...it purely slides in bottom crease of seat, click your isofix in off your seat...now re tether over and down the back nice and tight... its added peace of mind more than anything...
others may confirm..
i think i put a for saley add up a while ago if you want pics of mine, do a search on my post history, not been on site much of late as moved house in to a vast restoration project..