Most monthly dividend paying securities are exchange-traded and closed-end funds. A lot of these are leveraged bond funds and alternate investment funds such as Tall Texan's.
I haven't seen many compelling reasons to own these funds. Many have high yields driven by leverage, but the owner bears the cost of the leverage. This is why many have management fees over 1%. My experience watching these only goes back about 5 years, but most weren't around before then anyway. They did well during periods of QE and lowering interest rates. However, as soon as QE ended they started cutting distributions and prices and income tanked.
I love dividends as much as anyone on here. My only monthly payer is Realty Income. Instead of complex funds that I cannot understand, I own a quarterly paying low cost dividend fund, VYM, and a basket of profitable companies that sell actual goods and services and pay a quarterly dividend. My combined portfolio of holdings pays dividends every month.