The IOGEAR does support 4800 baud - you just have to configure it with a terminal emulator instead of using the DIP switches. That's not why I have the baud rate convertor.
Sometime when I have more time I'll convert my hand-drawn schematic to a form that I can upload and show all of you. But in a nutshell, my first priority is to install the GX2150 VHF/DSC/AIS receiver that I recently ordered (and have not yet received) and interface it with my GPS/chartplotter setup. I also have a couple of SeaTalk instruments that I would like to interface so I can consolidate depth readings with everything else, and maybe
to enable track-mode on my autopilot. But the Seatalk stuff is just "nice to have" not "must have," so if the conversion equipment ends up costing too much I'm not going to do that part of the project.
The new GX2150 improves on the GX2100 by allowing you to set the DSC input to 38,400 baud, so it multiplexes the AIS and DSC onto one port if you run at 38,400. (There are other threads on this topic.) But Seatalk only runs at 4800 baud. So using the baud rate converter to interface with Seatalk allows me to use only one Bluetooth port at 38,400 instead of needing two at different baud rates. It also eliminates a multiplexer, since Seatalk has its own built-in multiplexing capabilities by combining multiple instruments (in my case, depth and autopilot) into one Seatalk chain.
That Miniplex device is real nice because it combines multiplexing, Seatalk conversion, and perhaps baud rate conversion all into one device. But dealers are listing it at $400-700, and I've already found the BT and baud converters for about $20 each.
I can't find any specs on the IOGEAR's power requirements. It comes with a 120v AC adapter, but don't know if the adapter outputs 5v or 12v, don't know the amp draw, and don't know whether the connector is proprietary. The USConverters one runs off of a USB cable, which means it's 5 volts and less than 500 mA IIRC, and obviously there are 12v USB converters everywhere. So I'm leaning toward the latter because of the same power issues that you mentioned.