I have no personal experience with Expedite but they're definitely grey importers, as they're based in Hong Kong. They have UK distribution but the original items are coming from HK. As they're significantly undercutting even HDEW their prices are little too good to be true, and reading around there can be issues with returns etc as their UK presence is little more than a warehouse. They're a legit company but being a bit shady with exactly how they're trading IMO.
If you want to go grey import, which is a perfectly good way to go if you're willing to trade a little extra risk for a big saving, I would stick with companies like HDEW or Flash Camera, as even though they're a bit more than the likes of Expedite they have a long track record here of good service (which I can personally vouch for) and both definitely have UK-based offices.