I can’t seem to get it to work and I think it has something to do with the edit action button as it doesn’t display the one-click upsell for my product! 
And as well in funnelish, the tab I chose to link the page says its a downsell although on clickfunnels it an upsell, but i don’t know if that even matters
That’s really awkward the option to pick a product should be there, but could be the template you picked doesn’t have it or something…
I saw similar cases where changing the template helped showing that option if not you can simply follow this tutorial: Using Clickfunnels' "#yes-link-multi" with Funnelish PayPal Apps?
Yep, there is a huge difference, in Funnelish you should select Upsell if it’s an upsell, as Downsells are only shown if your customers say “No” to the previous offer if they say yes they’ll get moved to the next Upsell not skipping the downsell.