I have the Flame Boss 200 and have had no major issues with it. Both probes have failed one time, and they sent new ones out immediately, under warranty. New probes are only $20, so very affordable after the warranty expires. I have used the Flame Boss on a WSM 22, and on my Humphrey's Weekender. Works fine on both. The last few cooks, I'm getting a "Low Battery" notification from it, and it isn't using a battery. I searched the Flame Boss site and found that this typically indicates too low a voltage from the extension cord the unit is plugged in to. The gauge of the cord I'm using is a size or two too small. I can easily purchase a heavier cord, or make one... I just haven't done it yet.
One or two times, on major holidays (Thanksgiving), their servers were overloaded (too many folks smoking turkeys) and couldn't handle the load. They sent an email to all Flame Boss owners apologizing, and promising upgrades to their hardware, so it doesn't happen again. I believe they were genuinely upset that their system failed.
Their customer service has been great when I've talked with them on the phone. I believe two brothers started Flame Boss together, and one of them answered the phone a few times when I called (about new probes, and with help connecting to wifi). He was helpful and friendly.
I have no complaints about Flame Boss, and would buy another Flame Boss unit today if I needed one.