Hence in a single-engine you can fly the whole approach at Vref (or 1.3vso) if you wish.
That could be very unsafe especially if the manufacturer has set the minimum approach speed higher than 1.3 Vso.
Please remember that the approach speed selected by the manufacturer for certification can not be less than 1.3 Vso. It can be more.
The performance A aircraft (like the citation) does not have a single engine comittal height. Therefore it is entirely possible (and safe) to fly a single engine approach and execute a missed approach at 1ft. Are you saying that you would fly Vapp all the way down if you were OEI?
If you want to talk multi engine you need to pay more attention to Vmca and Vmcl which may be more critical than Vso