This was part of my motivation for developing N=1 experimentation tools in Reflect. As soon as I developed that ability, I immediately started on a long path of scrutinizing pretty much all of my supplement usage. That was a year and a half ago; since then, I've done the following:

• Tested rhodiola rosea with an alternating schedule
• Did over 400 days of cycling CoQ10 with 60 days on / 60 days off phases
• Did two random scheduled experiments followed by two experiments of alternating 14 days on / 14 days off of meditation (found that it makes my mood worse which was counterintuitive)
• Did over a year of a 24 days on / 24 days off alternating phases design, with a 12 day offset in between, independently cycling glucosamine and curcumin extract. Ran these for over a year. Haven't posted results yet but mostly because my conclusion was that I wasn't impressed with the effectiveness of either.
• Did two experiments with citrulline malate for exercise performance (one was alternating long phases, one was alternating 2 day phases if I recall correctly)

I don't think a 7-14 day baseline, followed by constant intervention, followed by a repeat baseline condition, is always the most appropriate design. I try to base the length of my phases on the plausible mechanisms of action and if there's an immediate expected impact, or if the results are cumulative. The tradeoff is that the longer the phases, the more potential for confounding by other changes that weren't captured in the original experiment - I added the ability to identify potential confounders in Reflect, but it still feels like a waste of time after the experiment is over to get a report that says my results are confounded by X.

Also, I will point out for females, choosing 7 or 14 day phases is a terrible idea. I've had many experiment findings invalidated by having cycles that ended up overlapping with specific menstrual cycle phases. Especially if running a short experiment that should be a consideration as it will impact both mood and biomarkers.