Essential Coffee Grinder Features
Grinding Just Before Brewing Impact
Coffee ages like any other food product. Here's the main difference between ground coffee and coffee beans: roasted coffee bean has a hard thick surface like a shell, like a vacuum container that cans its internal products. Coffee beans protect their content from contact with atmosphere, most importantly from oxygen and humidity. As soon as you crush open the beans you release oils and all other fragrant contents they possessed and you can actually enjoy smelling and tasting fresh coffee.
The exposed surface area of coffee increases dramatically when beans are ground. Once you crush your beans their content becomes open to air and humidity. Now you have just a short time to use the grinds well, i.e. prepare your coffee.
If you buy ground coffee you might think you taste real coffee because it was packed in a vacuumed box directly after grinding and you would be partially right. However packs aren't that reliable and you will not use whole coffee from the box at once. You will store coffee somewhere not that environmentally friendly. Best practice: grind only as much coffee as you will use at the moment.
Essential Coffee Grinder Features
I couldn’t deny that any grinder is better than no grinder. The taste and aroma you will extract is going to be greater than any kind of pre-ground coffee could provide. Prices of mills vary from $10 for the simplest blade coffee grinder to $2000 and even more for a burr commercial bean grinder that is usually used in cafés and restaurants.
Two major factors of the game: grind consistency and heat produced by a coffee grinder.
Frictional heat. Rotating parts of the grinder contact coffee beans, cut or crush them and thus create frictional heat. Excessive heat burns the particles and oil of coffee resulting in bitter taste drink. A simple conclusion: the less frictional heat a grinder creates the better. Blade coffee grinder spins at uncontrolled high speeds. To crown it all, ground coffee gathers together and opposes the blades. Keep the blade grinder on for too long and you'll receive the bitter taste. Remember - bitter coffee is not equal to strong caffeine drink.
Meanwhile burr grinders (whether flat or conical) rotate relatively slowly. Even though burr grinder will hardly burn any particles, some professionals prefer manual mills. You would have to put in some work to get your drink with a hand-crank grinder but some people prefer this physical pleasure. With a manual mill you wouldn't produce a single burnt coffee particle (correction: unless you can rotate the crank at more than 400rpm).
Grind Consistency. Are you still reading? Here's an advice: forget blade grinders. They will chop your beans into uneven sized coffee particles. Coffee ground in this way clogs coffee maker filters and it is not suitable for anything more than pour-over coffee.
To make a decent espresso at home you should be considering investing about at least $100. Cheaper models just won't provide the necessary consistency of grind so much needed for good espresso or any other coffee drink which uses espresso as the base (for example cappuccino).
Conclusion. All in all, it is not recommended to buy blade coffee grinder unless you are truly short on cash. If you can invest about $250 for a coffee grinder, by all means do so. However if you prefer drip, French or even Turkish coffee and espresso or cappuccino is not your drink you can find a decent coffee grinder for about or even under $100.