Cees,
Bram van de Stok indeed flew the 234 on the 10th of May 1940, but the Dutch pilots didn't have their own aircraft. On his first flight on May 10th van der Stok (03:00hr) flew the 233, with which he shot one Bf109 (and most probably damaged an other). On his second (06:15hr) and third flight (12:00hr) he flew the 234. However this aircraft was hit by German fighters during take off and caught fire. There is a picture taken by van der Stok from his burning aircraft at de Kooy. This is the only picture I could find from the 234. The 233 was damaged beyond repair during an attack around 08:00 and was used for spare parts.
After the 10th of May van der Stok flew several aircraft including the 221, the 235 and the 240.
Source: Fokker D.XXI - History Camouflage and Markings by Frits Gerdessen ans Luuk Boerman.
Daan,
Nice gadget, this opens some interesting possibilities!
Cheers,
Huub