To be clear, I only helped with the documentation. I think it depends on what you want out of the modulation. The toggle essentially selects from two predefined rates. A RATE pot instead allows greater control over the modulation. There's no right or wrong answer. The classic DMM design has the toggle set-up; the RATE pot is a modification. If you find that you think you'd like finer control of the modulation rate, go for the pot. If you think that the DEPTH and preset speeds would be sufficient for you, go stock. Keep in mind the stock build is a more straightforward process too.
Personally, I went with the pot. However, I've also built a Total Recall with the switch and have an old (unmodified) big box DMM.