Ok, when you have one sparkler, it is an utter joy to light and write your name in the darkness and whatnot. Well when you have two sparklers side by side, the effect of each sparkler is magnified slightly as the heat from each helps the other to burn faster, and thus send out more sparkles albeit a little faster.
Now take 50 sparklers. Tie all of them together, and stick one out the top. Do a 1, 4, rest effect if you want. Light the first, it'll go down and light the next tier, the next four will go down and light the other 50 or so. It is just amazingly pretty when the massive lump of them go off. As like I said sparklers have a sort of exponential thing going, the more of them, the larger the sparkle radius and so forth. The effect of about 30-50 is around a meter radius of sparkle that goes off in around 10 seconds, the end result being red glowing hot
It's as safe as any other firework (i.e, it's a stack of explosives kids like to play with), but gives you a feeling of accomplishment equal to the size of the bomb.