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There are many blade grinders in the market, and they are usually cheaper than burr grinders.
I've almost always heard and read that burr grinders are the best choice for most of coffee preparations.
So, is there any advantage —besides cost— for blade grinders compared to burr grinders?
You can use a blade grinder for nuts and spices as well, provided that the 'chamber' and blades are 100% stainless steel. It's pretty easy to clean the oils that would otherwise affect your next batch of beans.
That's not the case with a burr grinder, especially the ceramic variety - a hand-full of hazelnuts in one of those will mean anything coming out of it picking up that taste for quite a while.
I use my blade grinder mostly for that these days, since I own several burr grinders. Great at grinding up peanuts, dry corn kernels, dry spices and that sort of thing.
To clean it, I wash it with a moist cloth as usual and then use a moistened antiseptic towelette (like they use to wipe your skin with prior to giving you an injection) - there's no trace of what I just ground in it once I'm done.
The most important distinction between blade and burr grinders is the result:
Blade
Coffee beans circulate across the spinning blades. No matter how long or short the grind, there is extreme heterogeneity in particle size--that is, you will find larger bean fragments with near-dust-size ones, with everything in between. If you use a pour-over or drip brewing method, you might even see whole beans floating to the top. Not surprisingly, you'll get very uneven extraction from these different particles, no matter what the brewing method.
If you grind long enough to decimate all the beans, you'll find a lot of fine coffee dust and sediment in your cup. Too short a grind, and you get a lot of beans and bean pieces that can't present enough extractable surface area to the hot water, leading to a thin, weak cup. Waste of coffee, to be sure.
Also, it's almost impossible to grind any two batches consistently, since grind time is dependent on bean quantity, type of roast, variety of bean--well, everything. So today you'll get a disappointing cup, and tomorrow you'll get another disappointing cup for some other reason. Therefore I recommend a Conical Burr grinder.
Conical Burr
Beans move through once. When you set your burr grinder to a certain fineness, there will be very little heterogeneity in particle size. (N.B. Spend more on the grinder, get a more even grind.) This allows you to experiment with the grind as well as the quantity until it's perfect for you, then replicate that recipe perfectly every time.
Some tips on finding the right burr grinder for your needs:
Blade grinders are a bit easier to clean. Generally you can simply wash out inside and it doesn't require the disassembly cleaning a burr grinder does.
Blade grinders are also less likely to be damaged by inappropriate use or coffee that contains foreign objects (it's been known to happen as urban myth).
From the book Coffee: A Guide to Buying, Brewing, and Enjoying, I remember reading that if you use flavored coffee beans in a burr grinder, that flavor is not going to come out, ever. But with a blade grinder you can grind flavored beans, clean it out, and use it again with unflavored beans.
They take up less space than the burr mills than I've seen. An exception would be this little guy but if you want a fine grind you'll be cranking for a long time.
I'm under the impression that, for drip or pour over, the extra consistency of a burr mill doesn't make a huge difference. That is, while a finer grind will get you more extraction, a little variability in the size of the grounds is not the end of the world.
