Just an update on the inspiration: the link to the product I copied can be found here. I copied more than I remembered, all the way down to the name! However I stand by the purpose of this project, to open source a design (and also to make a design that doesn't require modifying the PO).

Further design analysis looks like the voltage converter is an LM317 or something similar. If this is the case (big if) then there are numerous possible advantages:

1. Using a switch-mode regulator can offer improved efficiency.
2. Using an LDO means that the small voltage drop from 5V to 3V wouldn't cause any problems, which may be using a linear regulator.

The part (LTC3405) I am using instead does have several negative aspects though:

1. Only 300mA output current as opposed to over an amp. This doesn't matter significantly for two reasons: USB is spec'd to supply 500mA so we're not losing much here, and also the PO only draws 30 mA so this would be enough to supply many (where other issues like noise would become a bigger issue).
2. More expensive. There is no way around this, the LTC3405 is almost $4, and $1 on the output inductor. To me this is a benefit though for efficiency and improved functionality. I like to have good accessories for my musical instruments.

Specifically, the LTC3405 has a mode designed for operating at very low current draw which is attractive as there may not always be a PO connected. Further, the designed as it is at the moment disables the LDO if there is no jack present in the DC connector. Both of these prevent wasting energy.