It's actually a second such event. The previous one was September 28-29 2013 and I got the invitation to join then too. The Tallinn event is straight after the Helsinki one (they travel to Tallinn on 25th and the test drives are on 26-27). I'd have to say, the empirical evidence that they created the second Helsinki event as a single day event suggests that demand in Helsinki region is low? The Tallinn event overwhelmed they scheduling multiple times over so likely they will shortly create another event to accommodate those who couldn't get a drive in the first, but six months later and only one day seems like Finns are a bit cold on this front oddly...
Demand in Finland might be low. Auto-Outlet is also offering test drives. So maybe this Tesla event is not so interesting for test drive point of view?
And I wish we would also have some incentives like Estonia. Could help a bit...