IMHO, the issue that so many people have with thunderheads as opposed to other fixed blade heads of similar size/design is the o-ring that comes with them. When you screw them down, the o-ring does not always stay where it is supposed to, and can be compressed right out of the side of the head/insert interface. This can lead to alignment problems.

If your heads are spin tested, and spin true, they will perform just like any other head with a similar design.