I have a problem with the category filters on Hotspots.
I have created a location in a sub-category, but when the map opens, it automatically ticks the top level category, and not the sub-category, so the location is not shown. Obviously this can be changed manually once the user goes to the filter and either clears it or selects the sub-category as well. However, many user won't get this far, and will just assume there are no locations in that category and move on, so the default should show All categories and sub-categories to avoid this situation.
By the way, I think you have created a brilliant extension in Hotspots. It is in my opinion by far the best mapping extension available for Joomla. I have tested the others and they don't measure up to Hotspots.