Well as a 45 year machinist, toolmaker, engineer, NASA scientist, I have to say that there IS a difference in cheap vs expensive end mills, BUT you won't notice the difference very much in a Home CNC.
Let me explain. Carbide is carbide. really doesn't matter if it comes from China, Japan, or Germany, its HARD. It is also a cemented material, and this is the difference. It's made from little tiny balls that are packed in a mold and fired. The SIZE of the ball does make a slight difference on a HOME CNC, but for the most part, difference is largely seen or felt cutting things like Titanium, PH Stainless steels on high end ($500k UP) CNC machines, using MICRO grain (Nice word for tiny balls, really).
Coated end mills are another thing. The coating generally is not there to aid in the cutting edge as much as it is there for a lubricant on the gullets (or flutes) of the cutter. This added lube stops sticky material (Aluminum, copper, etc) from sticking to the cutter. Because one the gullet is full of chips, the cutter will break very soon thereafter.
I tested some 1/4 and 1/8 cutters from Carbide3D with TiAlN (sometimes called AlTiN) coating and they are GREAT. For some reason they have been slow in putting them in the store. I can cut for days without anything sticking to the cutter.
I also highly recommend that if possible, use router bits for cutting wood (It really IS a router). They tend to be sharper then an end mill (which is designed for metal, not wood).
So in closing, I recommend buying CHEAP EBAY Coated End Mills for cutting Metal, and wood router bits for cutting wood (where ever possible)
Hope this helps a little.