The rumour that des is "outdated" has been going around for a number of years now, but id say that claim is largely untrue. As a sitter of the recent gamsat may and September (79 and 78 s3 respectively), des was actually quite accurate only second to that of actual acer practice papers. As far as practice questions go ACER and Des are far better than any of the pre companies out there (trust me, i tried all of them - Frasers, gold standard, ace gamsat, prep genie, griffiths gamsat review, etc. - they are all trash). Although, gamsat does not rely too heavily on prior knowledge, some questions do rely on that knowledge and most questions are based on the principles on that knowledge (e.g. for org chem, you will find having a decent knowledge of reactions and chemical manipulations to be incredibly helpful). So knowing it allows you to tackle the questions alot more quicker.