2. Why has nobody designed an app that lets you pay for groceries or a coffee, or any good in any store, with bitcoin, right there and then?
What I'm getting at is: What use is it as a method of payment if people can't use it on a daily basis and the transactions are so slow to get confirmed?
my answer is :
1. as far as i know, bitcoin is super fast maybe more faster than credit cards, as long as there is an internet connection that connected into blockchain, then it will work.
2. i think there is online store that accepted bitcoin as their payment, for the coffee, i know that starbucks is receive bitcoin too, i remember there is a thread in https://bitcointalksearch.org/topic/2017-01-01-dcebrief-ipayyou-launches-bitcoin-direct-to-starbucks-1735935, its an app that lets us to pay for starbucks coffee and other starbucks offerings.
i am sure that in future, the answer will be completed so bitcoin user can used their bitcoin for buying product in online store and offline store. soon the transactions will be fast to get confirmed and before that, all we can do is use the normal or higher fee for each of transactions we make.