While brewing in small batches can be just as much work as a 5 gallon batch, it is a good way to tryout a recipe. A small batch gives you flexibility w/o picking up more equipment. The key with small batches is precision. In a 5 gallon batch .1oz of hops isn't a big deal. In a small batch it can make a big difference.
check out
this Basic Brewing Video episode for an idea of how much work a 1 gallon batch is.
I've been doing a bunch of 2.5 gallon batches for an article I'm putting together on AG brewing in a Mr Beer fermenter...Besides blowing the dust off the Mr Beer keg I've been using a couple of 3 gallon water bottles as well...
I cold crashed a batch in the mr beer in my fridge Sunday, it fit fine. I haven't tried with the water jugs, one is really squat so it might fit....So you could lager easily with one.
And I'm not sure of the dimensions, but the 3 gallon better bottles, if you can find them, might fit in a frige as well, they're square sided, so 2 might even fit.
2.5 gallons are great, I can do AG full volume boils right on my stovetop, the average cost of an AG mini batch has been $15.00 and you end up with a case of beer...I did three last week, played around with a style I really didn't want a ton of beer of (Blonde/Cream Ales) and will end up with 3 different case of beer....
And if you haven't gotten AG yet, you can do it with a 2-3 gallon cooler, a folding steamer and a grain bag, you don't have to rig up a ball valve/ss braid (though it does make it easier.) A 2 gallon cooler can fit 4 pounds of grain, and a 3 gallon can fit 6 pounds...Like hops, that might not seem like a lot when you are doing a 5 gallon batch, but that's a pretty good sized beer for a 2.5 gallon batch.
Not a bad deal, imho.
If you wanted to do the mr beer keg route rather than a water bottle/better bottle, I bet you could get a couple cheap/free from other home brewers...I almost gave mine away to a buddy who likes the mr beer...Then I decided to keep it around to experiment, and now I find myself really getting into the whole small batch thing...I'm going to experiment with a couple more beer styles in a small batch format.
One hint, get a digital scale that measures in grams as well as ounces...some of the hops amounts are kinda difficult to measure unless you convert them to grams... One of the recipes called for 1/16th of an ounce....