Zodiac have fiddled about with the names and subtle design changes over the past 15yrs that can make the air floor range confusing.
In the Cadet range (i.e. not the sportsboat type like the Futura) the first air floor models just replaced the wooden or alloy hard floor with a high pressure air floor but the low pressure sausage keel was retained. This was inflated through a "hole" in the air floor in the same way as the hard floor boats had a cutout left.
Then after a few years they developed a deeper high pressure keel which was connected to the air floor by a hose and it all inflated as one. These were called Fastrollers or Acti-V models and broadly speaking replaced the previous low pressure keel models in the 3m+ size.
I've owned a 360 Fastroller in the past ( Zodiac Fastroller 360 Acti-V mini-review
) and currently have a 340 model ( Zodiac 340 Acti-V & Mercury 15 2-stroke Mini Review.
). In my opinion there is a slight improvement in directional stability and ability in a light chop with the high pressure keels.... but not enough to choose the HP keel over a LP keel if other factors were important.
After the HP keel design was introduced the LP keel remained on the sub 3m models for yacht tenders etc.
For 2015 Zodiac have reintroduced the HP floor with LP keel in the 3m+ sizes with the name Cadet Aero.
In a broadly similar size the Aero models are about £250-£300 cheaper than the Fastroller type.
I can't find the exact spec sheets online but the overall performance and carrying capacity of the two types is likely to be the same in real life use.
If you are looking at an inflatable around 3.5m then you only want 5 people in it for a very short distance in calm conditions... as a tender from larger craft to pontoon for example. Once you get out on the sea any distance in this size of craft then 2 adults great, 3 just OK, 4 more than you want and 5 emergency only.