Hi, The brevet is, in my opinion, quite right. A word of caution though. Most RAF issue brevets were carried as stock at 14 MU RAF Carlisle until the seventies so to find a long obsolete brevet in mint condition is far from impossible. Also, for Other Ranks up to and including Warrant Officer, the badges are a free issue item on change of uniform etc. However for Officers, they can be either privately purchased or purchased from RAF stock. This means that theoretically, when privately buying a brevet of any designation, the buyer can purchase from any manufacturer, tailor or collector's shop. So to use quality and condition as criteria for authenticity is quite incorrect. I have seen some very spurious looking brevets worn on both uniform and flying suits etc. Another thing to be borne in mind is that "in theater" insignia will also turn up and some of these items look totally wrong but aren't.
Hope this is of interest to you
Cheers Michael D