Just no to Alienware.
Its just dell crapware.
But beyond that, its not like they are manufacturing hardware. They are buying the same shit that is available to an end user. And they don't really pass on any volume discount they might get. And they charge you more for assembly and tuning. And usually, they hardware they use is not the best. Or at least not optimal for your needs.
In short, buying a pre-made PC is a scam, pretty much no matter who the vendor is.
Nowadays, building a PC is almost completely plug and play. The hardest part is picking out the components. The actual assembly is like legos.
And because these companies don't actually manufacture any of the hardware, there is no real advantage to buying from a 3rd party. It might be a whole different story if Nvidia and Intel teamed up to start selling computers, but that just isn't the case.