Just to share. I have been travelling around Penang using MyTeksi application. The driver who accept the booking have to use the meter. After reaching your destination, you pay driver according to the meter reading. MyTeksi app will email you the e-receipt.
The app is very user friendly. You can see where is the taxi and how long more it takes the taxi to arrive. You can even see who is the driver and the taxi number. Some prefer uber and i have read reviews that uber is also good for taking taxi in Penang.
If you try to flag the taxi or go to taxi standard, the driver will quote a price. The price is usually more expensive than meter one. The taxi driver on the road will not use meter.
There are traffic jam on the road. Has asked driver who said that peak hour is "7am to 9am" and "5pm to 7pm". Avoid these travelling times especially going to airport for departure.
Have tried taking Rapid Penang bus. They have unlimited rapid bus rides for 7 days for tourist @ 30 RM. Good if you want to explore Penang or take airport transfer via Penang Rapidbus
There are a free shuttle bus that bring you to Penang Street Art and Penang attractions in Georgetown. The bus makes many stops. see this link
http://www.penang-traveltips.com/cat.htm for bus route and details. It is totally free for tourist.
Malaysia school holiday is like Singapore. Shall not go place that requires to queue on Sat and Sun.. Eg. Penang Hill.