Police never used flip ups when I was there - some forces had problems with shell/hinge area cracking. We stuck to full face - a lot quieter.
New BMW System 5 appears to be very good helmet - have used both S3 and S4 in the past and liked them both. Very quiet, designed by BMW but manufacturer by Schuberth. At around £350, good buy, with flip down sun visor etc. For radio use, I have stuck to full face.