Upcart—Cart Drawer Cart Upsell

The app and UI is very nice. Very easy to use and it does convert. The problem is, many times there is a 1-3 second delay in seeing the item in your cart. It makes me wonder how many sales are lost because of this issue. Hopefully they can solve the lag issue because I'm not sure it's worth the upsells if I'm losing sales altogether from the lag.