Swale (which includes the island) is an area of high deprivation, and there hasn't been much investment for a long time.
Work on the island is basically the docks, three prisons and a load of caravan sites, so, to afford the house, you would probably have to work off the island (reliant on the bridge and traffic is often bad as a lot of the populatoon works on the mainland. Not sure how often the trains run these days).
That said, there are some decent beaches and open spaces (a lot is marsh).
If I had £850k to spend, I would probably spend it elsewhere, though, as neither the location or house are to my taste.