Even if an investment is capital guaranteed, your capital is practically not guaranteed due to inflation.
Normally capital guaranteed investment has lock-in period, for example 3 years.
If you have put your investment in FD for 3 years, it's 3 X 3.7% = 11.1% gain but if you put in capital guaranteed investment, you practically lose this 'guaranteed' return of 11.1% from FD, and worse still, you lose your money value through inflation as well (although same to FD).

But of coz, you might gain higher than FD if the investment works well.

So it's up to you to take the risk!