The name Oyster card was mentioned in Visit London as best ticket for London trip. So I took a look into it and decided that we needed one.
We arrived at Heathrow Airport in the afternoon. Follow the direction to the Tube. By the end of the tunnel and just before entering the underground station we found the ticket machine. We tried to put it on a credit card but it was rejected. And it only worked when our friend used her debit card. We weren't sure whether the card was rejected because it didn't have chip on it or simply because it was a credit card.
Not like Singapore MRT, the Tube's fare differ depending on what time of the day you're taking it. I found the fare table pretty complicated. Not to mention that they also implement similar zoning system like Vancouver, Canada. I guess the Tube has bigger area to cover and is way older than Singapore MRT.
The fare is cheaper when you use Oyster card compare to single use ticket. Not to mention it saves you time because all you need to do is tap your Oyster card when you need to as oppose to buying ticket each time you need to get on Tube. Though if you're there only for a day, buying a day travelcard could be an option as well. More travelcard information can be found here.
There is a 5 GBP deposit for each Oyster card purchased but you could request a refund at the end of your journey along with whatever fares that you didn't use. The refund ticket window is at the entrance of the Tube station at Heathrow Airport.
With Oyster card it saves you time instead of trying to figure out which ticket to purchase when you're at a ticket machine. We were there with a local friend but even him seemed to take some time to figure out which ticket to buy for us. Imagine a tourist doing that.
Oyster card also saves you money compare to single trip tickets. For a trip from Heathrow to South Ealing Station (which was about 5 or 6 station away) the difference was about 3 GBP. That's quite a saving.
If we have a chance to travel to London, I would go for the Oyster card again.