I’ve used it a couple of times, but it was a while ago now, and it was a bit different then. They’ve updated it fairly recently so you now have 60 days to mull it over, and you get a refund instead of a swop (which I think I’d prefer). Here’s the blurb: 
Sex Toy Happiness Promise
If you’re not completely happy with a sex toy you have bought from Lovehoney, let us know why within 60 days of receiving it and we’ll give you a full refund.
To make a claim under the Sex Toy Happiness Promise, fill in the Returns form above and choose ‘Sex Toy Happiness Promise Claim’ as the reason for returning the item.
The number of refunds you may receive under the Sex Toy Happiness Promise is limited entirely at Lovehoney’s discretion.
Please note that lingerie, lubes and better sex products and bondage items are not covered by the Sex Toy Happiness Promise
Read the full terms & conditions for the Sex Toy Happiness Promise.
We sent ours back simply because we didn’t like them (not powerful enough, and disappointing). They do decline them sometimes, but I think that’s to do with how often you may have claimed?