Are they REALLY needed to load ammo? No. Are they darn handy when loading? Yes. Of course just because the book, manufacturer or what ever said to use whatever as a OAL does NOT mean that will work in your gun! A friend was having problems and measured the .223 ammo and it was the right length for that bullet, etc., it just wouldn't chamber. What was wrong?! I said either the case was not resized properly (he said it was), shoulder/neck crumpled from over crimping (he claimed it wasn't), OAL length wrong (in spec), then the ogive has hitting the rifling, set it a .01" deeper, if that didn't work, another .01" until it was right. Guess what? THAT worked.
Also they are just plain handy to have around and fun to use. So yes, get one. In fact as rcmodel pointed out (the first thing I thought of too) is Harbor Freight has them for $10 and they are perfectly good and well worth the money.