There has been a lot of press coverage about investors losing money in accumulators. The regulators have chipped in with comments as well (largely to the effect that commercial matters should be resolved between the banks which sold the product and the investors unless mis-selling or other misconduct is alleged). Needless to say, investors facing significant losses and margin calls are alleging exactly that.
During the boom times, accumulators were very popular products sold by banks (mostly private banks) to clients (mostly high net worth individuals). I totally fail to see why the typical investor would have any interest in such products. Here's why. The accumulator is essentially a series of rolling put options written by investors on terms that oblige them to buy shares at a discount to the market price at the time the contract is set. If the market moves sideways or rises only a little bit, it's a good deal in that the investor ends up buying the underlying shares at a discount to market value. However, upside is limited because the accumulator will knock out if the price of the underlying rises by more than a very small amount (a 2-7% was quoted in the papers). In the other direction, there is huge downside risk if the underlying shares fall.
In short, the accumulator offers some benefit in a mostly flat market. It offers little upside. It offers a lot of downside.
It's a dumb product and I do not understand why most investors would be interested.