I have one. If there's more than one person in the household, you want the largest one you can find. Mine holds roughly 1 gallon of oil. That's enough to cook for 2 people. Anything smaller, and there's not enough thermal mass to hold the temperature. And, it's limited to about 1200 or so watts in a normal kitchen.
Most people get those smaller ones, and when they start cooking, say, french fries, the temperature drops a lot and the fries are cooked at a lower temperature. As a result, they end up absorbing more grease. The higher the temperature, the less oil that's absorbed by the food - thus the importance of not cooking a lot of food at a time, hence needing a bigger deep fryer.
Cleanup - wait for it to cool sufficiently, and put plastic wrap over the oil reservoir, then put it away with the oil in it. If you do things like french fries (there's a recipe thread here for french fries; more in a moment), no problem. If you cook a lot of crappy frozen pre-breaded foods, or put bread crumbs on things, then fry them, you end up with a lot of sediment in the bottom after 2 or 3 uses. After it settles, dump the "good" oil into a container to hold it, then dump out the remaining oil with sediment into whatever container you can dispose of it in. I simply wipe down with paper towels & soapy water. I've left oil in the thing for a month or longer with no problems. I almost always use peanut oil - buy it in 3 gallon things for turkey fryers, but use it for the deep fryer instead. When it's time to replace the oil, the oil thing gets cleaned with easy off. Cleans up fairly easily.
Best french fries: hand cut into 1/4" size (or even slightly smaller). Get a big pot of boiling water going - enough to cover the fries by a couple of inches. Dump in a couple of glugs of vinegar (I almost always use cider vinegar; cheap by the gallon). The vinegar does something with the acidity to keep some other reaction from happening which would make the fries turn to mush. Boil them for 5 or 6 minutes. Drain & allow to get fairly dry - doesn't take long since they're so hot. Deep fry at the highest temperature (375 on many fryers) for about 1 1/2 minutes. Then, choice: freeze and fry at a later date. The freezing causes cells inside to burst, making it even creamier inside. Else, wait a few minutes and fry the second time for 1 1/2 to 2 minutes. 1st time I did this, I doubted it would be worth the bother. It is. Besides, with a gallon of oil, the fryer is preheated to temperature just about the same time the fries come out of the water, so it really doesn't take much more time.