use lettings method

app/components/log_summary_component.html.erb

@@ -3,11 +3,11 @@
     <div class="govuk-grid-column-one-half">
       <header class="app-log-summary__header">
         <h2 class="app-log-summary__title">
-          <%= govuk_link_to log.is_a?(LettingsLog) ? lettings_log_path(log) : sales_log_path(log) do %>
+          <%= govuk_link_to log.lettings? ? lettings_log_path(log) : sales_log_path(log) do %>
             <span class="govuk-visually-hidden">Log </span><%= log.id %>
           <% end %>
         </h2>
-        <% if log.is_a?(LettingsLog) && (log.tenancycode? or log.propcode?) %>
+        <% if log.lettings? && (log.tenancycode? or log.propcode?) %>
           <dl class="app-metadata app-metadata--inline">
             <% if log.tenancycode? %>
               <div class="app-metadata__item">