I can understand the user's point .... if baking soda was in fact required, then it should be on the label, but I do not believe that to be the case and that the bottle instructions are more than adequate.
If you are going to use a base solution in there to counter the acid one, then what you you then use to neutralize the base solution from the sodium bicarbonate .... another acid solution ? If not, then if water flushing is adequate for the base solution, it should be adequate for the acid solution. I am not saying a base flush isn't a good thing ..... AFAIK it may be helpful in removing something else commonly found in a rad. However, one day while working in a lab, someone spilled some sodium hydroxide pellets which I helped picked up, later was wiping my sweaty hands on my pants and what I didn't realize at the time is it wasn't sweat., it was my skin dissolving. When those pants were washed the places where I wiped my hands were simply gone. If you do flush with a base solution as an added step, I would strongly advise a water flush in between as an acid / base reaction could be rather violent.
You will also notice that any medical remedy to getting splashed with mild acids or bases is flushing with large amounts of water.... sulfuric acid, the addition of soap is helpful for skin exposure and with that nasty hydrofluoric stuff a mild baking soda solution helps.....carbolic is not diluted by water and alcohol is recommended first and then water. For eyes, it's always just water.
Getting back to rads, if we were talking about an acid solution, that is the water in the rads, then the only way to lower pH on an acid solution would be to carefully add a base compound and bring the pH up to a neutral level. However, we are talking about resdue on metal here, and any industrial process that uses water soluble acids on metal for etching or other purposes is simply flushed clean with water. I used a vinegar solution and left it in for 6 hours..... I then flushed with alternating hot and cold water at about 4-5 gpm for about ten minutes, followed by three fillings with DW each of which was left in for 10 minutes with a "shakie shakie" action about 4 times during the period. I then used a pH meter, use a swimming pool test kit if unavailable, and got the expected 7.0
In short, while using a base solution is something I would not advise against, unless of course you did flush with copious amounts of water as you'd do for an acid solution, I'd say that Mathems instructions or more than adequate to obtain a neutral pH and not degrade their product.