This is a great value add service and very reasonably priced (fixed / locked in pricing is a winner, we all know how dreadful London traffic can be)! Especially useful when arriving after a long flight, takes away a lot of hassle if you have a driver waiting for you at arrivals.

While this is certainly a welcome addition to reach Heathrow, there are some things I'd like to mention on cost comparisons.

1. The fare for Heathrow you mentioned GBP 25 is when you buy it on the Train. The online/ticket office far is GBP 20. It also offers Group discount for return travel if you are travelling with kids or even 2 adults travelling together

2. If you book a cab on websites such as Kabbee.com or other comparable Taxi consolidators it costs anywhere between 25 to 35 quid (fixed price) for a standard car with upto 4 passengers and 2-3 large suitcases to reach Heathrow from the city (around 45 quid from Heathrow to city). I have used Kabbee on numerous occasions and have experienced no issues.

Welcome to AusBT, navnov! Thanks for your thoughts.

You're right that there's a discount when buying in advance or at the window. But that's not always possible — I know I've made the decision to fork out the extra fiver to make the train rather than waiting in the queue a couple of times now.

And travelling in on the Heathrow Express definitely isn't good value if there's more than one of you, unless your meeting/hotel is at Paddington station.  

Kabbee is one of those services I'm keeping a beady eye on — I've heard both positive and negative things about it, though the price is certainly very competitive. A common theme in what I've read and heard seems to be cancellations with under 24 hours' notice, which would be a big problem for anyone arriving on a longhaul flight. I'd probably have more confidence in an airline-backed arrangement, even if it were a bit more expensive.

Who'd want to fly Etihad Economy Class in the first place.  I just did Cairo - Abu Dhabi - Kuala Lumpur in December.  I will never fly on one of their planes again.  Crammed up like battery hens, both flights were horrendous.

I flew from Melbourne to Cairo by Singapore Airlines in Economy and the contrast was very evident.  For the time being anyway, SIA treat their customers with a lot more respect and provide a modicum of comfort.  Etihad couldn't give a damn.