I've had fast track outbound security at LGW as part of my lounge access in the past. At the time I went through there was no one waiting at the regular security channels, so it was money wasted.
Coming into LGW a few days ago, the E-gates were quick. People queue behind the first few gates at the head of the barriers, but weren't going to the ones at the top right that were empty!! We were off the plane and out within 15 minutes. Even when I came off a long haul and had bags to collect I was on the platform waiting for a train within 25 mins. Maybe the issue is LHR and the need to have more staff in general. With Advance Passenger Information required, they know how many people are arriving and what time so they should be able to do the analytics and staff it right.
HAL is very good at monetising everything and is constantly looking for ideas. If they could charge you for breathing their filtered air, they would. I don't agree with fast track like this because I feel there's always the risk that they will slow down the other queues to make people buy a fast pass. Fine if you've flown premium cabins, but then what if everybody starts buying it? Bit like some places where they have no free water so you have to buy bottles of it.