Paragraph 253(1)(a) is impaired driving, so the officer has to have evidence beyond simply that there was alcohol in the ambient air that would give the suspicion to follow a different avenue of investigation, not a 253(1)(a) investigation, but the 253(1)(b) investigation for being over 80 milligrams.
This tool is intended to help with the investigation of 253(1)(b). I don't see that it helps the crown to advance their case, if they're simply saying that well, they had deemed suspicion, but they're pursuing the 253(1)(a) actual impairment offence, because all you're showing is that there might have been alcohol in the ambient air, deemed to be alcohol in the body of the accused person. It doesn't take you very far on a 253(1)(a) charge.