The setup was experimental and not put into production. It was hard to load and set up, and it wasn't effective at all (intended for strafing ground troops).
Even the Lancaster and some other bombers tried similar setups. Almost all were abandoned as it really was just a dumb idea.
Yeah I figured experimental, I love reading some of the wackier designs some countries come up with, I can only imagine this version was made for a strafer of some sort for runways or ground troops, interesting because the IL-2 already had cluster bombs which made more sense to me.
I've always been interested in parasite fighters, for blimps and bombers - funny little things that never seem to work out.