Shiny app in bookdown book: iframe or link

I have started to write an interactive book on statistics with bookdown. I have included some Shiny and learnr apps. At the moment, I have included these apps via iframe.

I fear that my shinyapps.io resources are consumed whenever a reader is on my book website, even (s)he is not on one of the chapters with a Shiny app.

So I wonder if I should only provide links to exercises on shinyapps.io instead of embedding them with iframe? Or is there still another (better) solution?