Not in person but I've read some negative comments plus the price is not "right".
I don't think there will ever be a quality GF for less than a $1,000. The OCGF may be the lowest priced. The cabinet needs to be insulated. It needs to be built from at least 1/8" steel with the firebox getting 1/4" steel.
I came close to buying the OCGF, in fact, if there had been one in stock here in OKC I'd probably own one today.
The primary issue I had with it was air flow, because of how they directed the flow into the cook chamber with a baffle. The most negative comments I've read involves the air flow, some saying it took hours to get up to temp and if the cook chamber door was left open for anytime, it would take a long time for the cooker to recover.
On the MB560, the firebox is below the cook chamber, so the entry port for air into the cook chamber is level. The only restriction is the manifold. It has good air flow. That's how a GF should be built.
Some say putting an ATC on it solves the problem. Maybe so, but I think its in the design. First, the baffle directs hot air down, that's not good. Hot air wants to rise. And then the baffle forces it through two 90* turns, that's not good either. Flowing air likes curves, whether its A/C duct in the house or exhaust headers on an engine.
My plan was to take it to a welder and have that baffle re-worked to something similar to what Southern Q does with the Limo Jr. Which has a baffle and directs air down, but its one large 45* angle. I would bet a welder would rebuild the baffle for less than $200, maybe a lot less.
The only other problems I've seen, are uneven heating side-to-side, which I think a better designed baffle would help solve, and ya have to find one that the cook chamber door is a good fit. The only one I've seen in person had a huge gap in the upper left hand corner, which seems to be common.