SV1BDS I'm using a design similar to yours, it is sold in DL by DH1ND (see his QRZ.com page)
My combination of Helix-feed and LNB works well, a little bit better than a POTY feed for RX and a little worse than separate TX and RX antennas. By "a little" I mean differences less than 3db in RX, I noticed practically no difference for TX. When transmitting in SSB I sometimes see a "ghost signal" on the waterfall but my receiver is never desensitized.
73 de Greg