There are three primary units: Arctic Air, Icebox (phillip) and b-kool (bob stephens). Common features:
All three use an insulated cooler such as an igloo or similar.
* High output fan (cfm)
* Radiator or similar for heat transfer
* Water pump (small marine bilge pump) to move water around the system.
* All work on 12v or 24 v.
How they work - you can go to the icebox website for the details, but simple explanation: ice a water at the bottom of the cooler, pump pushes cold water thru the radiator, ambient air enters the cooler from vent A, then is then pushed from the cooler thru the radiator and the cooler air comes out vent B that can be directed. Water from the radiator returns to the bottom of the cooler and the pump cycles the water around. Repeat.
The size of the cooler and cfm (cubic feet/minute on the fan) determine pretty much everything. I'm sure a bunch of posters will chime in about the BTUs and such, but I'm not that interested about it, but you may find it interesting. Phillip (icebox) has all sorts of research, tests, graphs, etc. on his website. But what it really comes down to: The larger the cooler & the better insulated, the more room for ice & water (the coolant) means the longer you'll have cool air. There is really isn't any other magic or criteria.
Arctic Air has 3 different sizes (30, 38 & 52 qts). I forget the size of the Icebox (38-44 qts?), and I think the b-kool is 28-30 qts.
I've tried both icebox & b-kool and my primary consideration is size. Living out west and the type of flying I do means I'm not always near an urban area or airport. As such I carry a fair amount of emergency equipment. In the summer this includes either a 4 or 8 gallon water tank (also works as excellent ballast for CG) as well as the emergency bag, tools, oil, etc. in the baggage area of a cherokee. I can't fit all that and the icebox/arctic air in the baggage area. I've tried. Altho I have a bench back seat, it's not flat, so there's no way to snugly fit the icebox/arctic air.
This is a concern to me because I often fly animal rescues and need one or both areas for crates or dogs on harnesses. Which means the cooler must go on the front right seat. I don't feel comfortable with a cooler the size of icebox/arctic air in the front, even with it strapped down.
I used the icebox last summer on a flight from Denver to Devils Tower (about 3 hours each way, cruised at 9.5/10.5) Used the cooler for takeoff & landings and it was great. But....I didn't have animals or pax with me, didn't need all the gear since I was pretty much following major roads with lots of airports on the way, and I could put the cooler in the baggage area. I'm trying the b-kool unit (physically smaller) but it's May in Colorado and still snowing!
This is why I asked where are you going to put the cooler, and how much room do you have.