Myles,

AO51 435.300 is right hand circular polarization (RHCP). AO51 435.150 is left hand (LHCP). If you try to hear a LHCP signal with a RHCP antenna that is really right hand, you will have a drop in signal that can exceed 20db. This will make the downlink unreadable at low elevations. You definitely want to have switchable polarization on UHF if at all possible.

The reason that people have a hard time hearing SO50 when they are using RHCP is that although the antennas are supposed to be linear polarized, they don't fare well on RHCP throughout the pass. I find that I have to switch several times between right and left in order to hear the bird throughout the pass. Before I had switching, it was hit and miss with that bird.

The two meter side is not as important to switch unless you plan to operate AO7 and VO52 which have downlinks on 2 meters. If you do operate those birds, you'll be able to do much better if you can switch. Switching the uplink on UHF on those birds sometimes makes a big difference too.

If you are serious about operating the birds, the investment in polarity switching will be well worth it.

John K8YSE