Availed careem service while i was on Karachi visit. Great service. Clean cars, frendly drivers, on time arrival, best fare rate.
The fare is almost the same or even less than those kali peeli taxi... for which you have to wait, search around, bargain and suffer the traveling... 
Only the last careem i availed was not good. Driver was rash.
I complained to careem with feedback. They immediately emailed back with apologies and also credited 100 rupees balance in my account as a taken of gratitude 

In Islamabad, only had to book it once while stuck in a meeting and had to reach back my office on time and office van was away. When I got out, careem was waiting and happy traveling...