First I'll say if you CAN get them rammed down the barrel so they and their patch is sitting down tight on the powder there is nothing dangerous about shooting them.
Some nice heated discussions have occured here about hard/soft lead projectiles and I think the jury is still out.
IMO in the hard/soft debate the soft balls will shoot a little more accurately but I don't have any real statistical evidence to back up that statement.
The only issue in my mind is the consistancy of the ball size. If there is a lot of variation in size from ball to ball, accuracy will suffer.
Most "shot" is created by dropping molten lead alloy from a great height and it solidifies in it's fall to the bottom where it is quenched by water.
At best this is a imprecise method.
For large balls like buckshot I don't know how consistant the size of the ball is nor do I know what the acceptable tolerance for #000 buckshot is.
I'm not sure they use the drop process to make buckshot or if it is swaged. If it is swaged in a die then the size should be very consistant. If it is "dropped" I would think a tolerance for its intended purpose would be something like +/-.010.
The only thing I can really suggest is go ahead and buy it. Measure 15 to 25 balls and see what the actual sizes are. If the variation is greater than +/-.003 it will be OK for plinking but not for serious target shooting. If it is +/-.010 you could sort it into groups by size, keeping the ones which are within a +/-.003 tolerance and using the rest to make sinkers. (You do fish don't you?)
This sorting process isn't as bad as you might think if you have a verner caliper. After you find the smallest size ball, set the caliper to a value .006 larger than that and lock the gage slide.
Roll a shot down the length of the jaws. If it falls thru it's GOOD. If it rolls off the end its BAD.