The seller says the cruciform base with rounded visor is justified because
"the difference is between a dragoon helmet and a wartime infantry helmet. This helmet has not been tampered with and not just the dragoon helmets had the cruciform base during the war years. There is more to these helmets than the opinion of one or two books. I have had a email from a dealer in Germany who has no problem with the helmet in this configuration and I will likely work out a deal with him if it does not sell."
He also states that the visor is attached via a round-headed stud behind the scales.
Hessian helmets with round spikebases in wartime exist, but a round visor as described here sounds fishy. Perhaps the dealer plans to restore it to the correct visor type.