I did not know pressurized cream whippers existed until just seeing a reference to one, which led me to do a Google search. I own a manual cream whipper, which I rarely use, because it is exceedingly difficult to remove the cream from the canister. So I just use the whip attachment on my mixer. I'm very interested in hearing people's opinions on pressurized whippers, and whether they can be used for more than cream.
Cream whippers cleaning is not difficult, but rather heavy going, as what you usually fill them with are thick liquids. But you can clean the canister with a bottle brush and then follow the tips given in this answer on cleaning flasks.
You'd also have to clean the tip and the o-ring joints, but it's easy to do so with the pressure of a normal water tap.
If you are planning to get one think that you might not use it many often but it will occupy space, and they can be expensive to get (albeit this is something relative to each person/kitchen).
They are useful for making really quick whipps or mousses. But for some non conventional foods (see below) you might not find people willing to try them.
There are many recipes that use pressurized whippers, not just for sweet whipped creams. Some of them can be as innovative and surprising as the deconstructed tortilla de patatas. It's one of the utensils introduced in modernist/deconstructive cuisine, such as Ferran Adrià's espumas. You can get many recipes in this page from one manufacturer.
I am expecting my whipping siphon in the mail this afternoon. They are obviously intended for creating whip cream instantly but I find that it's best to think of this contraption as a pressurized chamber which affords you many different culinary options.
Using the pressure will allow you to make instant infusions of different liquids and oils. The general rule of thumb is to put something porous in the canister with the liquid or oil you want to infuse it with and charge it with 1 or more nitrous oxide chargers and agitate it and let it sit for a duration of 60seconds and then with it standing straight up discharge the pressure as quickly as possible to avoid the liquid from discharging and voila you have an instant infusion.
It can also be used to aerate purees or sauces. Some sauces will need some sort of emulsifier or thickening agent added to allow it to hold on to the gas when dispensed but overall it's a pretty versatile tool for experimentation in textures.
My plan this evening is to use it to pressure brew coffee which will lessen the acidity level.
The cream whipped by NO2 is less stable than cream whipped by a mixer, and will liquefy rather soon. If you have ever bought a cream "spray bottle", you know how the whipped product behaves.
You also have to find a supply for the gas cartridges and store them somewhere. Most people don't have a problem with that, but if you are short on shelf/storage space, or don't want to pay for the consumable cartridges, this becomes important.