With so many undecided voters the message the polls are sending is, at best, that no-one has any real idea what the outcome will be. The poll cited in OP isn't really much of a poll anyway, as it's an opt-in rather than opt-out poll, ie only people who a) visit the website, and b) care about filling in check-boxes for the sake of it are likely to respond. One thing the Leave campaign has in abundance is passion for trying to get its voice heard as loudly as possible, and I suspect this is skewing the result massively.
But anyway. The biggest message the polls are sending are that supporters of both sides can't afford to forget to vote in the actual referendum. I'm not sure it's ever been truer that every vote will count.