What's a "broadband booster"?

It is a real problem. How well this device solves that problem is another matter. What it professes to do, like some other products, is QoS (quality of service) prioritizing, presumably based on type of traffic. It may well help in certain cases, but it's probably not a panacea.

Most routers (past like 2 years) have integrated QoS so there is no need to worry. It's good for VOIP but for other things its a bit of a waste.

I beg to differ. Lots of low-end routers have no meaningful QoS.

I would save your money if I was you! I would bet it didn't do a single thing apart from making people think it did. Like the tuned circuit on a piece of plastic that was meant to boost mobile phone signals. Load of rubbish.