What i've seen on the net so far: slot ports are very useful because they are easier to make with big port area than aeros, and they can be bent at the inside end to allow a longer length than aeros.
Slot ports that are very narrow and tall/wide (like very rectangular instead of more square-ish) may produce unexpected results however with output/tuning. More symmetrical shapes like squares and (even better) circles are believed be better, but there isn't really much research on this.
The most important part of the port designs seems to be the correct port area and allowing the port to breathe on both ends. As long as it is, it should sound great