Wondering if anyone has upgraded from the FM3 to an FX-III - is there overwhelming reasons to do so ? just wondering thanks much
They're different devices, serving different purposes. I have both. The FM3 is perfect for live work for everyday working musicians, and for simple to medium-complex presets, and for when you need a grab-n-go system for travel or fly-dates. The FM3 and a FC6 is a killer combination, especially with the OMG9 layout.
The AF3 and FC-12, is for the touring semi-pro to pro, or the full studio, where the sound MUST be uncompromising and money is no object and you have a rack.
There's a really good overlap between to two, especially when the FC-6 or FC-12 is attached.
In the every day real-world, the FM3 is capable of 90%+ of the AF3. I can't imagine a touring professional needing 100% of the AF3's capabilities and odds are good the FM3 will cover everything a working player needs. A studio could run out of slots for presets, but that'd be because they're not being smart about off-loading presets or using their non-Fractal effects processors.
You are really the only one capable of deciding which makes the most sense. I have both because... well, I "graduated" from the everyday workforce, and then the virus hit and I had to take some money out and that's where I directed it. The end result is, I love them both and the FM3 is extremely capable but it's not capable of EVERYTHING the AF3 can do. But, every time I start working on a preset I discover ways to make the FM3 do something close enough that I'm happy. They're both great units.
My opinion is, use the FM3 until you run into a situation where you can not get it to do what you want, then sit on it for a week and think about it, and then try again. Do that several more times, and, after that see if it makes sense to upgrade.