The one thing that is very important to understand is that yield ultimately does not equal return. These funds are structured in a way to provide more income for investors, but they will ultimately cost you returns in the future as the covered call nature of the fund will cap your potential upside.
I was criticized by the high yielding community quite a bit over the last 2-3 years as I was highly critical of these funds and felt a lot of people were buying them for the wrong reasons. Fast forward to today, and virtually all of them are underperforming their benchmark indexes by wide margins.
These funds paint the picture to many investors who don't understand them that somehow 1+1=3. It doesn't. Yes, you're earning those high yields, but you're giving up something in return.
If rates start to come down and utilities start to see a recovery in price, there is almost no question that UMAX will underperform.
For SMAX, it's an actively managed fund that just came into existence, so I can't comment much.
Overall, a lot of these high yielding funds are just being developed by fund managers so they can capture high fees while taking advantage of the obsession for yield among many investors.