In looking at this most interesting helmet, though again emphasizing armour is way outside my usual field of study, I could not resist trying to find out more on these 'lobstertail' helmets. I agree that this example seems more a piece to carry the image rather than functional use. The skull seems far too shallow to securely protect the head, and the neckguard projects outward too much (though if it is correctly articulated as the Continental examples, perhaps this is shown extended). The number of lames (articulated sections) in the neckguard here is five, most German and Dutch examples have four. The lack of washers and securing guides inside the interior is apparant as noted.
The examples of these helmets from the Low Countries and Germany were apparantly imported in number just before or during the Civil Wars, according to David Blackmore in "Arms and Armour of the English Civil Wars", Royal Armouries, 1990, p.17). He also notes that many of these have 'L' or 'M' marks stamped on the nasal bar.
The English versions of these helmets are as shown by Kronckew, and were called three bar pott's for the triple bar faceguard. The neckguard on these was usually comprised of simulated lames, rather than articulated as the Continental forms, as I understand.
Interestingly I also discovered that these mounted troopers were known as harquebusiers, as noted by Mr. Blackmore, which is yet another fact I was entirely unaware of.
Thank you for posting this interesting helmet Norman! Whether an authentic period piece or not, it is a good looking example, and certainly did compel me to look further into these, which is really why I'm here, to learn!
Thank you!!
All the best,
Jim