I am building a Kraken. I am wondering if anyone has used the Spirit Pro on the Goblin Kraken? Wondering if anyone has seen the drift that some are seeing with some other FBL. SAB is saying that the Kraken is very rigid and some FBL are not able to handle the high vibration frequency.

Spirit Pro is really resistant against high vibration.

Unfortunately, the construction of the main gearbox of Goblin Kraken is not really smart. The main gearbox is made of straight toothed steel gears. This causes in extreme high vibrations because the tooth are not really high precision quality. Why they have build this is not really clear. Maybe in next generation of helicopter there will be a better solution.

It appears there are some people using the Pro on the Kraken with no issue.

Yes, in many cases it work. Depending on witch Motor, Rotor Speed and Flystyle you have. But most FBL Systems work hard at there limit and sometimes this results in problems. The problem is not the low frequenz vibration. When your mechanik is correct there is no problem. The problem is the high frequenz vibration from the main gearbox. This disturbs most FBL Systems.