It kinda replaces a hydrometer, but not completely. They do have advantages though.
Doesn't work with alcohol, so for final gravity you either need to use an online calculator or a hydrometer, for a 'normal' beer starting at about 1.042 it'll read about 5brix (1.020) when it's actually 1.009. It does stop though, so you can at least monitor fermentation.
You still need to cool a boiling sample without letting it evaporate. Simplest way is to pipet a bit out onto a cold plate, then pipet from that onto the refractometer. Some are auto compensating for temp, but it takes time (the body of the refractometer and the wort have to reach the same temp).
I have both, they both have their uses. I'd prefer to use a hydrometer, but the refractometer is the more useful when sparging or for monitoring fermentation (and you don't want to lose half a pint every day checking it).
Stop being clumsy, a refractometer is a glass prism, it wont take kindly to being dropped either!
Now, what you really want is a Density Meter,
this one from Anton Paar should be OK, in fact it dam well should be for �ã3220 (plus �ã12 shipping)!
