I'm struggling to understand what products I should be using. Is there somewhere I can get the comparison between these products (and any others I may have missed)
My quick take:
@EconomiCurtis' answer was good. There's also a table you might find useful here: https://www.rstudio.com/pricing/ Scroll to the bottom. It compares different ways to deploy things you've created with R (shiny apps, r markdown outputs, APIs,...) including shinyapps.io and RStudio Connect. As Curtis said, rstudio.cloud is different - it's the RStudio IDE - but if you have a shinyapps.io account you can use those credentials to try out rstudio.cloud.