Looked this up as sounded interesting, found this..
“when you send them back, we will exchange them for a £5 gift voucher for you to redeem off a minimum £40 order at stores or online. Takeback vouchers are valid for one month. “
Doesn’t seem that much of an incentive to me. Think I’d rather give them to a charity shop, especially like one I use that is only one of two that supports a small local purely voluntary animal sanctuary, not a big charity that pays high salaries out of money they raise.