They are both fine to use.
Kryonaut was developed for extremely demanding applications, and has a higher rated thermal conductivity, and is not suitable for silicone sensitive applications.
Hydronaut was developed for users with large heat sinks, has excellent thermal conductivity but lower rated than Kryonaut,.. and is suitable for silicone sensitive applications as it is silicone free.
Both are not electrically conductive, and require no curing.
I recommend going with the Kryonaut if your overclocking, and for high long-term stability.
