I like their clean, classic design, I bought two in the late 90's, black with gold trim because I didn't know any better, mistreated the 18k nibs, eventually ended up buying fine steel nibs, which are nicely smooth: recent ones seem to have the exact same design, although others might correct me. They are my most temperamental pens but I finally enjoy using them:
- They evaporate like crazy, but I stopped knocking my head against a wall and just keep them in a case with a clear top (a Platinum case I think); of course this might not be as important to you; I have had no starting or flow problems.
- Not every ink gets along with them, even with this arrangement, I am now using Fuyu Gaki and Souten which seem fine. Lie de Thé came out really dry. In the last iteration I put a bit of cellophane between the nib and feed of the one with Souten and it finally comes out less dark than in every other pen I tried. So two unlikely renegades came together to get the job done.
- They demand to be used, if not they seem to want to slightly cling on to paper, which is also something that happened with my Pelikan m600; of course not everyone might keep 25 pens inked. They are easy to disassemble and clean, if need be, the nib and feed rotate out of the section, and parts are available.
On the other hand, they are heavily pirated, I wouldn't buy any Sonnet from China (not that there's anything wrong with China, if it costs less than $10 USD... it's a fake. A very good price for a real one might start at $35) and I would pay close attention when buying elsewhere. Some recent editions look nice buy command rather ludicrous prices over the more regular ones. So in spite of my odyssey, they are nice pens.
"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt."