I'm not positive on this, and someone that knows a bit more of the specifics should correct me if I'm wrong, but the $99 stick is using chips with 32x8 configuration. This is a "lower density" configuration, and as such, should work in the non-Via equipped mainboards that people have. I bought one of these sticks when they were $140 (I thought that was an okay deal at the time...) and I can verify that it runs at stronger memory timings on a CUSL2 (Intel chipset) and a Via KT133.
Chips with the 64x4 configuration, or "high density", may have larger compatibility problems. You save $20 if you have a mainboard that supports those chips, but depending on how long you want to use it, the lower density may serve you better, longer. I do not have a high density chip to verify memory timing results, but I can tell you that at 133, my chip does 2-2-2 7,9 on the CUSL2 and 6-2-2-2 on the KT7.
Your particular mileage may vary, but I certainly would say it is a good-excellent value.
