I bought a K40 while waiting for my Glowforge. I souped it up a little, added an air assist. When it worked it was the best $350 I’d spent. When it didn’t it was a 60lb paperweight. The single advantage I felt it had over the glowforge was its speed. The other advantage was a hard limit switch. Engraves were 2 or 3 times the speed of the glowforge. It was a real challenge to keep it running. Every once and a while it would get knocked out of alignment, requiring an hours worth of tinkering to get going again. I wasted a lot of stock trying to figure out where a cut or engrave would start. I figure I have saved a few hundred in materials costs with the Glowforge with the camera alignment.
If you are having condensation problems (which we are only guessing is warm moist outside air coming back in to the glowforge from the outside) you may need to install a blast gate. I don’t have condensation issues, but it’s about 20degrees out right now, and even with the dryer vent flap on the outside the inside of the forge will get very cold if I leave the blast gate open. They are cheap at Harbor freight, you can get better ones, even some that are automatic if you want to spend real money.
There is a bit of a learning curve for the software. I remember my first moment when I realized it wouldn’t engrave an SVG as a WYSIWYG, and getting used to colors instead of layers for operations was another hurdle.
The speed of the engraves is a bummer. I hear you. I almost cried when I realized how slow it engraves, even though I had sprung for a Pro with “Improved Optics” and “Faster cuts”. Maybe they can come out with a fixed focus head for those times you need the speed, but not the bells and whistles of the Auto focus head.