This is what the website says

If you’re an Avios or Choice Rewards credit card customer, you could receive rewards for you balance transfer subject to eligibility. Please refer to Help and Support for further details and conditions.

If you're a Choice Rewards credit card customer you’ll earn 10 Choice points for every £5 transferred
If you're a Duo Avios credit card customer, and opened your account before the 3rd November 2013, you’ll earn 1,500 bonus points for every whole £1,000 transferred. Bonus Avios are only awarded on whole multiples of £1,000s (£1,000, £2,000, £3,000 etc.) transferred from a single provider. For example, bonus Avios would not be awarded on a balance transfer of £900 or if the transfer is split between more than one credit or store card.
If you're an Avios Rewards credit card customer, and opened your account on/or after the 3rd November 2013, you’ll earn 1.25 Avios for every £5 transferred.


For me that means I only get 1.25 avios per £5