I have some Salter smart scales that talk to an app via Bluetooth, but I never use the app and tbh I rarely use those scales (instead preferring a non-smart Salter set) as the additional time to switch them on, open the app, get a connection, etc., is a faff.
I look at the back of the packet, do the calc in my head (or for meals/receipes with multiple components write them down on a bit of paper - which is useful when you don't know how much of the total you will eat vs other people). much quicker than selecting the correct item in the app, etc.
The difficulty with apps (or any sort of list) is if it doesn't have exactly the thing you're eating then you end up spending time looking for some equivalent with roughly the right carbs. For things like potatoes and pasta where the listed information is generally annoying (cooked vs uncooked, different types of cooking, etc) I generally go by eye anyway (as I split bolus so can correct later)
I bought the smart scales to talk to an app which is on my neverending todo list, hopefully I'll get round to writing it one day!