I've had my CHM/BRTRO 420 for 2+ years now, and was planning on upgrading it with Blair's Blazing BRTRO board (
https://github.com/bleckers/brtro-420-better-blazin/wiki), when the main controller died. The symptom was that, after heating, one of the elements would no longer turn off - which made for a batch of broiled boards before I detected the problem
I took the system apart, and found a toasted driver mosfet with burnt traces - a sketchy board design at the least. From Blair's blog on HAD, the controller uses an obsolete MCU, which reinforces the low cost driven nature of the machine.
In these two years, I've processed thousands of boards, and found a couple of issues/constraints:
The edges of the tray are IR shadowed, and don't reflow well. While I can fit a 3x3 array of 10cm panels onto the tray, I got many failed reflows on the outer perimeter - so I now only do a 2x2 array in the middle of the tray.
I switched to GC-10 leadfree paste - and getting the oven dialed in to handle it was a pain - the UI for setting curve temps and times is a disaster, especially coupled with the poor thermocouple placement and accuracy.
Now that it died, I'm going to replace it with a T937M - the larger tray should let me go back to a 3x3 panel array AND leave enough slop around the edges to avoid the cool areas.
-John