The word 'doubt' covers a universe of variations. Even a standard coal fired power plant has issues, issues that need to be solved and even change day to day due to coal supply changes. For real power systems there are always issues, bugs in electronics, pumps that wear, pipes that spring leaks, motors with bearing problems. That is life, it is normal for large systems, you work through them.
On the other hand, Tokamaks have a first wall problem that no one has an economic solution for even after decades of study. Helion does not have that. Diverters are a wear item, likely they can be refurbished, unlike retaining rings on a large electric generator rotor that spins at 3600 RPM and can develop cracks over time.
So, 'doubts' for Helion are, IMO, related to normal systems issues that are unremarkable, as opposed to real doubts that are remarkable for Tokamak projects. (Zap, General Fusion, TAE do not have a first wall problem, their designs avoid it).
I know of no issue for Helion that rises to the level of a project stopper, (other than regulatory). Polaris is a demonstrator for non technical investors, politicians, and those with an interest in denial, IMO.
Counting the days to commercial fusion. It is not that long now.