It'll help if you can clarify the conditions when you want to power that equipment. Power from the alternator while the bus runs? From the starting and lights battery? A house battery? etc.
If you'll be powering from the bus alternator then efficiency of the power supply system isn't a factor. Either the bus is motoring along down the road and a few watts lost to inefficiency of powering that equipment makes a tiny difference in fuel consumption, or else the bus is idling while you work and it's converting fuel to electricity as a horribly inefficient generator. In these cases using an inverter to power the ordinary mains power supplies is the most convenient, off-the-shelf approach.
If you'll be powering from any kind of battery and want to make that battery last as long as possible, running the equipment direct from dc with a power supply like the one you listed at newegg may help you get about 10% more runtime out of the battery as compared to using an inverter. The dc power supply approach could be more physically compact as well.