Unless the installer charges you more to install components that they didn't supply, such as "that mp3 player". I'll bet it's better to get components from the installer, if they have what you want. Starts off the service relationship on a good note and they're working with stuff they know. It's all about pleasing the service provider so they don't screw you over.
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FireFox31
110gig MKIIa (30+80), Eutronix lights, 32 meg stacked RAM, Filener orange gel lens, Greenlights Lit Buttons green set