One of the drawbacks of buying, at least for some printers, is lock-in. Some vendors attempt to lock you in to buying filament only from themselves in a similar fashion to inkjet printer manufacturers. I would steer well clear of them.

I've built a few. The major drawcard to me is the ability to tune, tweak and rebuild to get the printer I want rather than the printer someone wants to sell me. That and the upgrade path is again my choice, rather than the vendor's.