The advantage with tax lien certificates is that they are backed by real-estate, so there is little risk.
The government guarantees you the interest or you will have the rights to acquire the property for the back taxes and costs.
It is true that the percentages are against it, as about 97% of the time, the property is redeemed, and you will get your interest, and investment back.
When they are not redeemed is when you could literally get the property for pennies on the dollar.
How much interest can you get? A bunch. Take Illinois, where there is a 16% penalty for 6 month periods, so that is a yield of 36% if paid off in 6 months. If it is redeemed in two months, then the yield would be a whopping 96%. Try to get that from a savings account.
Same with Texas that sells the deed, but has 2 types of redemption periods depending on the property type. A 25% penalty on the winning bid amount, for the 6 month redemption period, which is a 50% yield if paid off the last day, or in the case of the 2 year redemption period, there is a penalty of 50% if it goes more than 1 year.
The penalty States are the best, as you can see. Other States offer a interest PLUS a penalty, so there are many opportunities.