Yes a 10" slider can be more portable and accomodating than a 12" or 14" fixed power miter. Blade cost is also a consideration. The 12" blades are spendy, the 14" blades are insane.
The better brands of saws will have less decflection (most fixed saws are just fine). If you get a slider, then get the Hitachi or DeWalt. The newer models are much more accurate.
If you are getting a fixed saw, then consider the 12" or 14" models. As mentioned dual bevel is nice, but not needed unless you are doing crown or other complex compound miters. It is not just a matter of flipping the board over. The dual bevel esnures that the blade does not cause tearout on reverse cuts.
$50 is cheap for blades... most good power miter blades run right around the $100 to $130. With few exceptions, you really do get what you pay for when you buy a blade.
If you just need something to cut wood with and do not do much intricate or precision work, then check out some of the harbor freight power miters (central machinery or chicago electric) they server their purpose and are not that bad at all. They are certainly not DeWalts, Makitas, Bosch or Hitachis... but they do just fine for the weekend warrior.
Bean