I can not really connect successfully to my printer via USB I have a Tronxy P802M (very similar to the Anet A8, but using a Melzi2.0V5 board) that seems to work fine (I just finished building, and axes movement and the integrated display work) but when I try to connect to the printer from my Simplify3D on Windows 10, I get the following:

[...]
  Connected to machine!
SENT: T0
READ: ok 0
READ: wait
SENT: M105
READ: ok 0
READ: T:24.44 /0 B:23.33 /0 B@:0 @:0
  Connection failed.


My other printers all connect fine.
The Simplify3D support site mentions to disable the "wait for startup command" option in the firmware configuration for S3D.

This allows me to make a rudimentary connection to control the printer, however e.g. during the bed levelling wizard of S3D, the connection still breaks off.

It works reliably with Octoprint. I'll consider that good enough.