It will be ok if you make sure the push pins are in good,... the weight is above intel's specs, but that doesn't mean it is bad.
The retention bracket is for those who don't trust the push pins, or just want a little more peace of mind. Keep in mind one thing though,... if you use the push pins, and move the case,... like going to lan party, actually moving to a new house or what not,.. you want to take a little more care to not just toss the case around, that would be the only real worry you should have.
Also the retention bracket can give you a tad bit more cooling with the extra pressure applied,... think 1-2 degree range and don't think of it as a deciding factor!!!
Hope this helps
As a disclaimer,.. I have the xiggy 1283, did use the retention bracket for peace of mind since I just moved, am in a temp location and will move again,... I also have to move the case a lot at this location,.... otherwise I am not sure I would have got it