havent bought mr beer kits in about 3 years.. yes, cheaper than buying craft beer by the bottle ready made, but cost per gallon at least for me was less practical than doing a 5 gallon batch. a 5 gallon all grain cream ale can be done for about 28 bux... 53 bottles of beer for 28 dollars. thats about $4 a 6 pack? i think. sales are always good.
Refractometer can be used before alcohol is created. After it's created, it's not accurate - but there are sites on how to adjust it.
Big, huge breweries that have very expensive refractometers also use a cheap hydrometer.