Quoted from EMsInKC:

To me, once again, proof that the decagon was not Gottlieb's finest hour. They're an unnecessarily complex design that is fiddly to work on and prone to getting out of adjustment. They're notorious for hanging up on the 9 due to the wireform pressure on the cog when the nine switch isn't adjusted just so.
At least in my opinion, compared to the Bally/Williams score reels of the period, they come in last. Bally and Williams reels are much simpler in design, much easier to service, and much more reliable in performance.

Quoted from newmantjn:

My issue is that they are built like crap out of thin thin gauge metal, IIRC self tapping screws etc., and they tend to rattle themselves apart.
The biggest ongoing issue I have with the decagons is that the EOS switch breaks off, but the way they were designed, you usually don't know, since it is somewhat redundant.