For decades asset managers faced a simple choice. The expensive option was active fund management – like eating at a Michelin-starred restaurant it can be delicious (as long as the chef performs on the night) but the bill is high. Or they could use index-tracking products – the investment equivalent of eating at McDonald’s: basic fare at rock-bottom prices.

There's a huge gap between these two options. So it's no surprise that when a new strategy comes along that could offer Michelin-starred cuisine at close to McDonald's prices, investors have been hungry to try it.