NavList:

The magnetic compass is still a treasured tool for the small vessel navigator, at least archaic ones like myself who also still carries paper charts as informative tools. 

By a magnetic compass I automatically assume it is properly compensated for deviation and if it is over a degree (you can't steer a whole lot better anyway), then a deviation table is available.

Why do some of us small boat navigators cling to that fritzy wobbly thing that can be upset by a magnetic screwdriver left on the dash:

Mark

You missed an essential one; why every small vessel needs a hand bearing compass: Checking if you’re on a collision course with another vessel. 

Also, it’s important to realise that deviation is a function of the position the compass, or flux valve is in, not the quality of the compass.  Move around with it, as in the case of a hand bearing compass, and the deviation will change.  Similarly, a large chunk of iron out of place near a compass or flux valve will affect the deviation of any compass, similarly a lightening strike, or a large change in latitude. DaveP