After some serious engine issues, I recently purchased a snorkel kit with the above pre-filter at Rami. AEV, Quadrateck, ARB and a few others make a model that is essentially the same thing with some cosmetic deferences. If you are interested in a detailed description of how it works I suggest checking out this link. https://www.youtube.com/watch?v=rcXt44LWxF0. In a nutshell the air intake slats are angled in a way that forces the air to spin inside the internal cone. The centrifugal motion forces the heavier dust and sand particles up and out into the outer collection area while allowing cold particulate free air down into the snorkel.
The only issue I have so far had with this product was my initial installation attempt did not fully seal the snorkel to the filter box and consequently a lot of sand was sucked into the stock filter. It is VERY important to use A LOT of silicon when making sealing the snorkel to the filter box, I mean when you think you have used to much...double your effort
.Another potential downside is that it only works effectively with completely boxed filter systems so you would have to get rid of most CAI filters.
Since I have had it properly installed I have had little to no sand in my stock filter, even after long desert drives. Another major upside is that my air intake temperature has dropped dramatically, typically to 10'C over ambient.
The below video link shows a AEV style filter in action. It has a slightly different mechanism than mine but the principal is the same.
https://www.youtube.com/watch?v=_P3u7wgiy-c
In my opinion these products are ingenious in their simplicity and are so effective that all serious desert off-roaders should consider using them. I would be very interested to hear from others who have one of these products and if they have experienced any problems.
