These people sell a wide variety of items, not just militaria-see their website. I don't have enough expertise in pickelhaubes to comment on the ones they have with any confidence,however my take on their British helmets is that for the most part they are genuine but very overpriced for the types of helmet and often the condition they are in. So much so that the same helmets have been coming round again and again on eBay for what must be years. I have no idea if they are naive, hoping to attract those with more money than knowledge, or hopelessly optimistic but I do wonder how they make any money!
Patrick