I have to offer a few caveats to what has been written above.
I have nearly a dozen examples of the M30/25/15 series, and in my experience over the last few years, the plastic can definitely crack. Three of mine have developed cracks, some not even from use, so the problems of differential shrinkage of early injection molded Pelikan plastics reported in the earlier 25 cartridge pen were probably not solved with this later seies. Perhaps this is not the best EDC pen.
The later series P28 and P478 Silvexas ( cartridge-only) have metal barrels and caps, but the thin clear plastic threads on the section are also delicate. They can crack, particularly if you are cranking down on the threads to pierce and secure the cartridge. And their nibs are even closer to modern Pelikan nibs in grind and reduced flex/spring.
other issues of note on the original M30 series: the Kovacs feed does work well, especially for an early injection-molded plastic feed--but if the nib begins to separate from the feed (as sometimes happens with these pens), it is not easy to remedy, and that lovely wet flow becomes intermittent and unreliable. There is a thread here discussing this problem, which others have experienced as well. A third issue is that replacements for the friction-fit piston filler have dried up, and no one is as yet making replacement piston seals if you ever need to service it (unlike the vintage 400 and 100n series). Some 60's plastics are holding up well, but often the plasticizers migrate, soft plastics get stiffer and seals begin to leak and piston rods can fail.
Most of these issues have been reported on earlier threads here. While probably a more reliable pen than the earlier 25, the M30 series is still not the tough, reliable workhorse that current model Pelikan 200/400 series are. And they don't write nearly as well as the magical 400 series nibs.
They are also skinnier than the 200 series, though well-balanced--in that sleek 60's Parker 61 way. For a smaller hand, they can feel great.
There's a reason why these M30's were once quite inexpensive. They became popular as a cheap alternative to vintage 400's, but at the current higher prices, the m30 series may not be such a great deal any more. A broken pen or pen that doesn't work may is not such a good buy in the long run.