I know ive seen Griffen single speed frames in the fixie circles, they made decent track bikes is the only thing i can think of with them.
joglo pulling their website it seems they moved away from MTB's pretty early on, though its probably a pretty decent frame. Downtube gusset and the... not bad but not good welds going on there makes me think its a pretty thick aluminum frame.
And then based on the components, this is someone who knew what they were building, and ordered a custom frame to begin with, its reasonable to assume its a decent bike.
If the price is right, id jump on it. Finding someone else's era built retro bike is not that common.