I’ve written negative reviews on testers before. As long as you explain what the problem is then the review will still be helpful. What you don’t like might be exactly what someone else is looking for or it might save someone from buying something that won’t work for them (which benefits Lovehoney too as they won’t have the potential return and the customer will be happy so more likely to buy again).
The important part of reviewing (for testers or products you buy) is being honest.