With all of that being admitted, I think there may be a place for the one day a month trading system, albeit requiring that the trader have a compulsively methodical attitude toward his or her money management tasks. Given that required level of oversight and control, this method might be profitably used in that portion of one's holdings which are in tax-deferred accounts, eliminating the largest handicap, higher taxes.
Further, it might be a worthwhile system to use just some of the time, when coupled with other seasonality factors. For instance, the time of the year we are in now, from May 1 through October 31, falls under the "Sell in May and Go Away" guidance, so named because most of equity profits occur from November 1 through April 30, but the remaining months (May-October) generally have more volatility, and hence more and deeper periods of losses, as well as showing lower overall gains. There are typically profits, but they are so modest as to be almost insignificant.
Thus, one might reduce risk in the least profitable, most risky 6 months of each year by employing the one day a month strategy only in that period, then being normally invested at one's desired level in equities (for instance 60% of one's liquid assets) from November through April. This way one will at least still have a shot at close to or above average equity returns in the riskiest part of the trading year but with far less exposure to risk than with the buy and hold approach.
And if one is a trader anyway, used to dealing with higher taxes due to short-term transactions, one might use the one day a month technique along with margin debt during the riskiest 6 months of the year, increasing one's potential profits then, yet without seriously increasing risk and costs. As a rule, I do not like margin debt. However, this strategy is so low risk otherwise that if one is careful and disciplined it might be one way margin could be profitably employed.