From the internet searches that I have done:
Monark users claim OEM quality the way it used to be (not the OEM India quality) and a quieter idle. The adds always say replace as a set indicating to me that there is some differance in their construction (perhaps how the pintel is ground or the nozzle hole size).
(I a guessing but the nozzles from my car have a tiny hole cross drilled at the base of the part of the pinte part that protrudes from the injector nozzlel; maybe the Monark nozzles do not have that extra hole in the pintels.)
Bosio nozzle users claim better than OEM quality and better "seat of the pants" performance when you step on the pedal and a little more or no reduction in noise at idle.
I have only read one bad article and it was in this forum concerning Bosio nozzles. The member had 1 of a new set of nozzles go bad and returned it to the Bosio rep. in the US and was told it was caused by the WVO use.

__________________
84 300D, 82 Volvo 244Gl Diesel

What most who have the old SD 240 design are seeing is the pilot injection hole. The purpose was to quiet the engine, and it did. BUT, this was designed when the rest of the car was not as well insulated as they became by the mid 1980s. The trade off is more fuel consumption and emissions.

The 240 design was updated to the 256, 261 and the last is 265. In some German manuals and catalogs each subsequent number is listed "for retrofit of previous" or something to that effect. I also saw one footnote for the SD 265 - "suitable for use with vegetable oil" but I was not able to cross reference that.

Monark are stock design, ISO 9001:2000 and TUV certified.

__________________
1987 300D (230,000 mi on a #14 head-watching the temp gauge and keeping the ghost in the machine)
Raleigh NC - Home of deep fried sushi!