What do you mean by investment option to save up a part of your income for the future? What if the future fall within the bear market?
When making an investment you do not leave a small window open for when you plan to take profits cause you cannot accurately predict when you would hit your preferred RoI.
If I bought Bitcoin as an investment and plan to hold long term, I can take that to be 6-15 years. At any point within those nine years I can take profit and if an asset stays in the bear for almost a decade it's not a terrible investment.
Every investor and investment aim is to make more money. If we are not interested in making profit other than the save up for the future, we can save our money in banks instead.
Fiat is a terrible option for savings. Bitcoin is designed to function as a Store of value and also as an investment, it now depends on what I want to use it for.