Ordered 5 items from MMS several years ago. Received 2 items after 3 days, another 2 items 10 days later and the final item a week after that.
Going by the amount of items they list, it is unlikely much is stocked on site, and the hamble office certainly isn't big enough to be called a warehouse. I expect orders are placed with suppliers for each consumer order, so lead times are way beyond their control, especially at this time of year.
From memory, all their online chat hosts are called James and there were loads of poor reviews at the time, but things seemed to get sorted eventually.
Happy when wet!