How affective are informercials?

Answer 1

The only people who are able to answer a question like this are the companies that produce and broadcast the infomercials.

What is clear is that they are effective enough to make it worthwhile to produce the content and then pay for it to be broadcast. Production costs will typically be many $1000s and air time will be charged for each time it is broadcast - that varies depending on the channel, the time, the estimated audience size among other things.

The profit from sales resulting from the broadcasts need to be greater than the costs. It is safe to say that the successful infomercials generate significant amounts of revenue.