In the past I have purchased 2 sets of Nerfs for the 400ex and they worked great, real solid. I also have purchased 2 sets of front bumbers for the 700xx. They worked real nice but the front bumper insert plates have 4 tabs/flange that screw to the bumper itself. These tabs over a short period of time break from vibration. I have broken tabs on 3 different sets of inserts. I finally put rubber washers in between the inserts and the bumpers. It held up for a little longer but still ended up breaking.
i have fitted a couple of sets of these ac racing nerfs to our quad, (customers bikes, not mine) and i personally dont like them, the nerfs with heal quards are a royal pain in the arse to fit but do work and just dont look right for some reason, where as the nerfs without heal quards are a even bigger pain in the arse to fit and just look weird, each set i have fitted the nerfs seem to angle up a fair bit and do flex alot if you put weight on them, but i suppose they are better than having your leg lunched by your tyres