Obviously the Diamant cruises and handles very well with the flaps at 0 degrees, and would do as well or possibly even better with no flaps at all (cleaner wing profile and thus less drag).
You listed some advantages, and I agree with you on these points. I would rather try to list the disadvantages of the absence of flaps to check if one of these reasons is important in your own case.
1 – Higher stalling speed.
2 – Higher approach speed.
3 – Flatter maximum approach slope.
4 – Higher landing speed.
5 – Higher take-off speed.
Number one and two are not a problem from my point of view. A higher approach speed can be seen as a rather a good thing on very crowded airfield…
Depending on the airfields to land on, number three can be very annoying. Some airplanes operated in mountains have no flaps but they are specially fitted with airbrakes… Some of them of very simple design are very effective. The landing speed is not reduced, but the airbrakes can lower L/D ratio at approach speed down to about 3, and retracted anytime when needed…
Number four means stronger undercarriage to survive to faster speeds on bumps, stronger brakes and/or longer runways. Not really a problem on a large nice airfield.
Number five means stronger undercarriage to survive to faster speeds on bumps, more powerful engine and/or longer runways. Again, this may not be a real problem on a large nice airfield.
However, the Diamant is designed to fulfill the French amateur built aircraft regulation (CNRA) and this regulation imposes the aircraft to demonstrate its ablility to fly over a 15 m (50ft) obstacle situated at 600 m (2000 ft) from the rolling start point.
On grass runway, at MTOW, with the less powerful engine recommended, a long pitch propeller designed for cruise and no wind, flaps may reveal quite useful. Of course, if the regulation that your own plane has to comply with is not so demanding on that point, no flaps can be a good solution.
As far as you maintain your proficiency at side-slipping, you shouldn’t need to add airbrakes.
I don’t to know if the Diamant has ever been built without flaps… and if flapless plans are available. Jean-Claude Piel (BIG) should be able to answer this question.
Les fourmis sont des guêpes comme les autres !