MDL RCKT ENGNS 3PC C6-5

What are the differences between this and other engine packs ( eg. A8-3 )? Can they be substituted?

do all 3 packs of engines a-3 thruc-7 comre with wadding and igniters plugs?

What is the size?

What do these other reviews mean when they say they lost their rocket? We think this engine burned ours up. Is that a possibility?