I am getting an interest boost of 2.5% and on the website it is displayed as 4.18% yearly interest and not 6.58%. As a percentage of my total balance it is only a 0.10% increase but as a percentage of the previous rate it is 2.5% higher.
For me the extra interest is not an important factor to consider when investing in FUN because unless you're a big whale who can deposit several BTC it will take more than a lifetime to earn back what you paid for these tokens from just the additional interest alone.
I believe that's not really that impossible but you are forgetting the fact that you also have fun token, which could be more valuable or not as well. So we are talking about something like buying a house, sure most of the time it would take maybe a decade for you to get back the house value from the rent profit you make each month, as a landlord you buy a house for 200k and rent it for 1000 and then you get it back after only 200 months. However the house is also now 500k after 200 months, you are forgetting that profit.
Of course there are other benefits to holding FUN tokens but for me getting additional interest ranks at the bottom of everything else. Getting reward points and sats from the wheel was the deciding factor for me when I bought these tokens.