The answer to this one is simply yes.
Yes you can and you are not on your own, there are plenty of other people doing it as well rather than claiming the free gifts.

When you claim a for example a free iPhone as a gift then the affiliate company can claim the tax back off it so can afford to pay you the full £20 per referral but sometimes you would rather have the cold hard cash and this isn't a problem at all.
You can claim your rewards in cash at the rate of £17 per completed referral.

Cash can be paid to you via Paypal or Bank Transfer and only takes as long as the verification process that is explained on the How does it work page.