I have a SR161 from Miltech Marine and it is a one channel unit (one
channel at a time, but it switch channels in some cases). It is good
to see the ships, but I think that if you want to have a unit with
good performance related to AIS Class B boats and want to see in
advance that very fast motor boat going into you, a 2 channel
parallel unit like the SR162 could be better, but it will cost more
than twice the SR161, which price is less than US$200.