Both the Duckworth Pro 721 2012 and the Duckworth Pro 723 2013 are modified-V designs, both built in aluminium, so the buying decision usually comes down to a handful of practical questions: how many people are you putting on the water, how far do you trailer, and what does your tow vehicle weigh?
On paper these two are close siblings in the size department - Duckworth Pro 721 2012 at 21,0 ft versus Duckworth Pro 723 2013 at 23,0 ft. At 1 600 lbs and 1 700 lbs respectively, both sit in a similar weight class - either should pair comfortably with most mid-size SUVs and half-ton trucks, though always confirm your specific tow rating with the motor added.
For family outings this is probably the sharpest distinction between the two. The Duckworth Pro 723 2013 is rated for 7 passengers, while the Duckworth Pro 721 2012 caps at 6. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Duckworth Pro 723 2013 could be the deciding factor.
Bottom line: Choose the Duckworth Pro 723 2013 if your priority is putting more people on the water - it handles 7 passengers and at 23,0 ft it has the deck room to back that rating up comfortably. The Duckworth Pro 721 2012 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 6 that costs less to run day-to-day.