Having read through Eon's loyalty scheme, my first thoughts are that if their prices are competitive there is no need to offer rewards. Customers would be glad to stay with them.
Depending on the length of time you've been a customer of Eon, rewards increase from between £10 to £20 for being a customer for up to 3 years. Rewards are not applicable for customers buying only one form of energy, however extra rewards are offered for managing your account online.
When you consider the cost of a year's annual energy consumption, at approximately £1200, the rewards are much less than 1% of the total bill.
Very derisory considering that customers can save between £100 - £200 by visiting a comparison website, and changing to the lowest tariff.
Regarding loyalty schemes generally, I have Boots Advantage card and a Tesco clubcard. As I use Tesco weekly, the value of points soon mounts up, and it's economical to save money on shopping when the vouchers come through. Also, with Tesco, greater value can be obtained with their vouchers if you purchase one of their offers.
Eon's rewards are definitely on the mean side, and the reward incentive would not be enough to earn my loyalty. I want to pay the cheapest price, not be offered a derisory reward.