They can be reloaded fairly quickly - They make a BP shot gun reloader tube that lets you carry pre-measured shot and powder loads. Pour your powder, put wad over the powder, pour shot and put an over the shot card to hold it. Re-cap the nipple.
I shoot a Pedersoli flint lock fowler and also have a Pedersoli 20X20 Howdah. Both are great and fun shotguns.