Most are the same but I have seen one with a different scale on it that I couldn't figure out - came to me in a box of random tank junk from another hobbyist.
You should be able to get a decent one in the $50 range. DO get the calibration solution with it. In recent years I never saw one that was correctly calibrated fresh out of the box. And do calibrate it regularly. It only takes a moment and it takes the guesswork away.
Once you go to a refractometer, you'll wonder how you ever manged without it.
BTW - the same type of refractometer is also used to measure the specific gravity of urine.
Jenn