I use a splitter and do not seem to have a problem with range. We 'see' ships at more than 20 miles. Certainly not a scientific experiment since there is no control for comparison with two antennas. The idea of having a redundant antenna is attractive though.
Heading back to Lake Ontario for this summer. Now in Bermuda and heading to Long Island Sound in the first week in May. Then on to the Hudson and the Erie Canal.