Best RX Practice: Choose With Side Effect or Use Subscription?

I am converting events (paging events from buttons) to IObservable and receiving the result from the service asynchronously.

As a side effect, I need to update the child mode. I have two solutions:

• Side effect when choosing:

      //Converting events to a "stream" of search results.
      IObservable<SearchResult> resultsFromPageChange = Observable.FromEventPattern<EventArgs>(this,
          "PageChangedEvent")
          .Throttle(TimeSpan.FromMilliseconds(500))
          .Select(async ev =>
           {
               var input = new SearchResultInput()
               {
                   PageSize = PageSize,
                   PageIndex = PageIndex,
                   SearchOptions = _currentSearchOptions,
                   SearchText = SearchText.Value
               };
               var result = await GetPagedComponents(input);
               //Side effect
               ActivateAttributesView(result.Components.FirstOrDefault());
  
               return result;
           }).Switch(); //flatten and take most recent.
  
        
  
          
          
          
        
  
      

• Do side effect on subscription:

      //Converting events to a "stream" of search results.
      IObservable<SearchResult> resultsFromPageChange = Observable.FromEventPattern<EventArgs>(this,
          "PageChangedEvent")
          .Throttle(TimeSpan.FromMilliseconds(500))
          .Select(async ev =>
          {
              var input = new SearchResultInput()
              {
                  PageSize = PageSize,
                  PageIndex = PageIndex,
                  SearchOptions = _currentSearchOptions,
                  SearchText = SearchText.Value
              };
              return await GetPagedComponents(input);
          }).Switch(); //flatten and take most recent.
  
      //Do side effect in the subscribe
      resultsFromPageChange.Subscribe(x =>
      {
          if (x != null)
              ActivateAttributesView(x.Components.FirstOrDefault());
      });
  
        
  
          
          
          
        
  
      

Both methods work. Which solution should I choose and why?

THX.

Because the question is why this creates values ​​at all, here's the complete code:

        //Converting events to a "stream" of search results.
        IObservable<SearchResult> resultsFromPageChange = Observable.FromEventPattern<EventArgs>(this,
            "PageChangedEvent")
            .Throttle(TimeSpan.FromMilliseconds(500))
            .Select(async ev =>
            {

                var input = new SearchResultInput()
                {
                    PageSize = PageSize,
                    PageIndex = PageIndex,
                    SearchOptions = _currentSearchOptions,
                    SearchString = SearchString.Value
                };

                return await SearchComponentsPaged(input);

            }).Switch(); //flatten and take most recent.

        SearchString = new ReactiveProperty<string>(""); //Bound to TextBox.Text 

        //Create a "stream" of search results from a string given by user (SearchString)
        SearchResult = SearchString
            .SetValidateNotifyError(s => _componentDataService.ValidateSearchStringLength(s).Errors)
            .Throttle(TimeSpan.FromMilliseconds(500))
            .Select(async term =>
            {
                var input = new SearchResultInput()
                    {
                        PageSize = PageSize,
                        PageIndex = PageIndex,
                        SearchOptions = _currentSearchOptions,
                        SearchString = term
                    };

                return await SearchComponentsPaged(input);

            })
            .Switch()
            .Merge(resultsFromPageChange) //Merge the result of paging and text changing.  
            .ToReactiveProperty();

        //Update Attributes view
        SearchResult.Subscribe(searchResult =>
        {
            if (searchResult != null)
            {
                ActivateAttributesView(searchResult.Components.FirstOrDefault());
                SearchResult.Value.TotalItemsCount = searchResult.TotalItemsCount;
            }

        });

      

        
        
        
      

    

This is actually sending a search query to the DB when the search string changes and getting page-by-page results OR getting another page with the same search string when the PageChangedEvent page is received. Does .Merge (...) include a subscription?