I talked to an owner when on holiday last year and he mentioned that it tended to go through the waves and that he needed his "spinning window" thing as you find on big ships to see were he was going when it got rough.
Many of those "dutch barges" travelled all around the North sea coasts.As did of course quite a few Thames barges which carried cargos to some most unlikely far flung places.Not sure why the Dutch chose that design of bow when we chose a more conventional stem for our version.Both very flat bottomed though to allowed access to shallow tidal creeks.
The Dutch barges are indeed capable (working) sea boats but not quite the same as what they call a vlet today. Mostly they mean a single level (or low) steel cruisers that will pass most of the low bridges. The earlier models had a bow resembling a dutch barge but some of the newer upmarket models have a more proper "boat" bow. I saw one out one the Belgian coast a few years ago and it seemed to be doing OK. More built for inland water though.
The website mentioned above I think is the best place to start. Vlet is a pretty loosely used term.