24ppm of the 100ppm dose rate, is not going to have a noticeable effect on the beer. Some german beers exhibit 3x that much in pale lagers(although you can CERTAINLY taste it at that point).
I would strongly advise against the usage of meta for de-oxygenation of tap water.
Why? Does it require the dose to be higher, or does it just not work?
If it doesn't work, period, I'd begin to question whether the meta is doing anything at all.
The most obvious answer is it's just a waste. Why, if you can get </= 0.5 ppm DO from preboiling and chilling and then protection against 20 ppm DO from 100 ppm dose of SMB, would you waste active protection for up to 60 ppm DO by using SMB to remove oxygen from your tap water?
Because preboiling and chilling 18 gallons of water is a bigger waste
You already have to take it to strike temperature so the additional energy is in taking it from say 160 F to a boil and holding it for a few minutes.
My water starts at 80 in the summer. Plus there's the latent heat of vaporization.
The molecules in liquid water are held together by relatively strong hydrogen bonds, and its enthalpy of vaporization, 40.65 kJ/mol, is more than five times the energy required to heat the same quantity of water from 0 °C to 100 °C (cp = 75.3 J K−1 mol−1).
Energy is obviously an issue but I'm more interested in time.
If I'm taking a shortcut like using SMB (which is not typical for any German brewer, let's be honest), I might as well go all the way.