Well, I do prefer round frame over square frame, but I would much rather be able to stop safely, so as the 3800 has drum brakes, that seems the most sensible option to me.

AFAIK all solexes have "normal" bike brakes, with a pedalbrake for the rear (pedal backwards).
My Oto, a dutch build 1700/2200 has got a drumbrake on the rear.
Just like my girl's 3800.

I wonder whether there's some Dutch strangenesses there...

My 2200 has rim brakes front and rear.
My (early) 3800 has rim brake front, drum brake rear.
Neither has a back-pedal brake.

Stop safely? You could just blow forwards and the things would go backwards
I had an urge a year or two ago and bought a 1964 3800 (or 3300 cant remember) ,although its not about speed or power and i'm used to 60,70mph capable scooters i enjoyed pottering around on it but the novelty soon wore off ,i had to pedal it anyway at the slightest hint of an incline and i got overtaken by a bicycle while going downhill flat out