SPI to USB converter Question (for STM32F105)
From the Aardvark page it comes complete with:

Aardvark SPI Host Adapter Unit
6 foot USB A-&gt;B cable
Software (downloadable from website):
  Windows USB Drivers
  Linux USB Hot Plug Configuration files
  Rosetta Language Bindings: C/C++, C#, .NET, Python, Visual Basic
  Examples
  Datasheet
  Documentation


Plus it is a finished product and they will even customize it with your own logo for you in order to promote your own brand. I'd say those are some pretty significant value added features.

The Sparkfun item is for hobbyists and is only provided as-is. You are pretty much expected to know (or to learn) how to use it by yourself. The software for it is all open source.

It seems those are the largest differences. The Aardvark requires a minimum order of 100 items.