I interviewed with Chaucer and though it was some time ago it sounds like they are still using a similar process. Although it was a little unusual, it was on balance a fresh approach and much better that the standard Big4 "run me through the CV that I have in front of me but have not read" approach.
The presentation was two pages in ppt and to be completed in half an hour. It is therefore not a major test of your ppt skills, but if you are good on it, then I dare say you'll make the pages sing a little. The main challenge is to be succint and think quickly as you only have half an hour and they are mega-strict on the timing.
When I did it the two pages were on separate topics. I do not want to disclose what these were as they are probably still using at least one of them and I feel it would be unfair to punish a firm that is taking an intelligent approach. Knowing the topics would give you a significant advantage because you could think through the content in advance, but conversely it is not necessary to prepare in order to do well.
Both the topics by definition will be familiar to you. This is not like case studies where you have to show you ability to hypothesise or extrapolate . Simply be prepared to quickly consider how much time to apportion to each page and then consider how much time to do basic bullet point and how much time to spend makign the pages pretty.
The interviews were much more standard, but of good quality, conducted by a relevant SME and a "manager"
For the record, they decided I was not right for them. I agreed. My overall impression of them was positive but quirky. They probably quite like that.