If you cant look after an ion, then chances are a DM5 will be way beyond you.
as for the manual, it tells you what you need to know for the basics of keeping it running. For everything else there is the internet. That applies for most markers, as interpretation of even an amazing manual (such as the ego) can sometimes end up being subjective. WRT Dms, there is never a concensus on say, the best lube, and in fact the dye lube that used to come with them was **** - so again, look to the net for more advanced help.
Ion regs are reportedly some of the best in the business. You should always chrono from day to day, and even morning to afternoon as ambient temperatures can affect FPS. Also I beleive there is a locking nut out there for ion regs.
FWIW the stock equipment on an ion DOES suck - but so does that on say, a PM5. The feedneck was ****, it had NO ASA, and the barrel was a 12'' one peice like the ion. and that was a mid-high range marker in its hey day.
Lots of people change or have to add items to their guns.
the ion has a decent board and useable stock equipment out the box so all you need to do is add air and loader. It comes with everythnig you need to maintain it. as for falling apart hmm dunno bout that. the ion i had was mint.