I have booked ola cabs many times. My experience was over all good. Some of the drivers are arrogant but others are very good and reliable.
The other thing good is that you can keep the track of the person traveling if they have registered your number. So it becomes a great safety measure specially for women who are traveling late night.
The fare is also quiet nominal. Only the surge charge they apply during peak up time is an headache.
But overall it is economical, safe, easy and reliable!