There are probably more but I have come up with two basic types of bobbin holders or bobbin rests. The first is a solid block of (interesting looking) wood with 2 – 5 holes drilled in it. Tapered drills are great for this, thanks to those bullet-head bobbins. From a design aspect a good (useful) bobbin rest will hold a bobbin upright with or without a spool clutched in its little jaws. Both my solid block and fretboard styles will do this.
The fretboard style bobbin rest(s) come in a variety of capacities ranging from three to seven. Seven may sound like a lot but I know folks that have no problem filling them up. Again, loaded or not loaded is important to tyers to have the bobbins vertical. The fretboards easily meet that criteria thanks to the lower shelf I install for just that reason. Lately I have begun adding 3/16” holes to some of my spool racks to hold bobbins. If there is space available on the piece why not make them as handy as possible? Ahh, its that innovation thing again!!