I have been using CNG in Karachi for 2 years... Also had the experience of going to Thatta and Karli (Keejhar) Lake on my FX. I found these pumps good and bad are listed;
1- Farzand CNG - Rashid Minhas Road, besides Lasania Restaurant
2- Royal CNG - Malir, Near Anwar Baloch Restaurant
3- The pump CNG pump on the road which is going from Practical Center towards Rashid Minhas Road, just before Rashid Minhas Road, also less price (58.xx) when it is 63.11
4- Makli CNG (Thatta)
5- Shell Pump, first one on the left on Shara-e-Faisal after Drigh Road, going towards Nursery. Also membership available for FREE services like car wash(cool one), wheel alignment etc. on 15 and 30 refills.
1- Shell opposite Millenium Mall, Askari 4. Worst of them all, bad service, bad pressure.
2- Shell just before airport (pressure good, but no pre-set, they manually stop the machine on the asked amount )
3- Most PSO pumps
4- All Manual pumps, where they need to stop the filling manually, this way it sometimes charges you 1-2 rupees extra and it's annoying if you do not have the change at the time.
I'll update the list when I come accross more.