When I did a couple of hours of trial for Eurostar I got a free return ticket to Paris. Definitely a good investment of a morning. I can't say I'm tempted by the DART trial.
Ahh but did you get a free bag, pen and writing paper all covered in Dart logos and a free lunch? Well actually the lunch cost £300m
The next trialists will forgo the lunch.
At 16.5 miles the Heathrow Express is still a luxury when you can get a Zone 6 railcard much cheaper.
Which makes Luton even more expensive but the Dart will be a good experience.