A look at their loan book shows that a lot of their loans are high risk with predatory interest rates. The reason they’re able to offer high rates of return (relative to other P2P lenders) is because of that increased risk. Although you might have strong returns during a good economy, these type of loans are the first to default when the economy struggles… a recession would almost certainly hurt substantially. If you are to invest with them it should be a small part of your portfolio (the size relative to your appetite for risk).
Personally I wouldn’t touch this because of the interest rates, I would not want to profit from the predatory nature of payday loans. Loans are usually a good tool used to the borrowers benefit, payday loans unfortunately are not, they frequently take advantage of vulnerable borrowers. Payday loans are more than 30% of their business, and 20% of their payday loan borrowers are late on repayments.
Here’s their statistics: https://www.mintos.com/en/statistics/
 Some countries have somewhat reasonable regulations around payday loans but many countries do not, and looking at the countries on this platform it looks like most of these loans will be poorly regulated (or not regulated at all).