do you know how much fee they charge?
i think this is equivalent to buying the index and then the corresponding equal strike leap put.
the fee is about the value of the put
either bond and call, or index and put, are similar concept.
What I think is that to capture the uptrend, buying index is low-cost and straightforward.
Puts are generally cheaper than call in a uptrend. Also I think they may be able to take into consideration that most of the time stock market goes up than down, then they may be able to achieve the goal by buying fewer put to protect over the long run, e.g. only equivalent to 1/2 of all the index purchase, if they have enough costumer over a long time span to average out the risk.
补充内容 (2018-11-16 10:04 AM):
just checked again. Puts actually are more expensive than calls. so you are right, maybe it is bond+deep in money calls, and the bond payment is used to pay the time premium for the calls?