I have bought a Formula 6 Driver and 3 wood from eBay and a Formula 5 4 wood as well. I have hit the driver and 4 wood much straighter that I have hit anything else in the past. However, I will say this I don't have a lot of experience testing out other clubs as I didn't play much for about 10 years. I enjoy playing equipment that other people haven't heard seen before. I was curious about them as well and found a decent deal and took a chance.
I did build some hybrids with Formula 6 heads the 22 degree and 25 degree with some Matrix Red Tie shafts that I found on clearance. I hit them a long ways but I have absolutely no idea where they are going, but that as been the case for any hybrid that I have hit.