Fisherman,
Bosch or Beru are of equal quality and should not have caused any differences in starting. Monark plugs seem to have a shorter life span though. Perhaps you have carbon in the prechambers, which should have been cleaned by reaming before installing new plugs? If the old plugs didn't fall out in your hand - meaning you needed to tug on them to get them out, then you need to clean the prechambers. Excess carbon will touch the plugs and soak heat away from the plug, reducing their effectiveness. It's also possible you got the wrong Beru plugs by mistake. (??)
Another nice tip is to install an afterglow-type relay AND plugs. This keeps the plugs hot for 5-30 seconds after startup, reduces smoking & shaking drastically, and emissions too. It's not cheap ($100+) but sure is neat.
The "poor-mans" method for OM617.95x engines is to remove the purple/violet wire from the connector on the glow plug relay. This is the "start" signal that normally turns the plugs off when you release the key. Then they stay on for the full 30 second maximum every time. This works great, except they also light the plugs for 30 seconds on each hot start, so it will drastically shorten the life of your plugs - UNLESS you get the afterglow-specific plugs, which are designed for 30-180 seconds of afterglow. I did this for the winter only, now that it's warm out I'll re-connect the wire. Note that the true afterglow kits have a temperature sensor that reduces afterglow time for hot starts, saving the plugs. Some people do the purple wire trick & connect it to a wire on the dash, which is fine, but usually doesn't fly if it's your SO's car!
Regards,