Hello Mr W,
I have had a boat (23') at Parkstone Bay for the last 3 years.
The first 2 years I had a swinging mooring as you suggest - worked very well for me. Access it pretty much at most state of tide as you dont need to enter the shallower marina, altough LW Springs can be a bit tight.
They offer a free Taxi servicen which is a HUGE boon and saves rowing out - however tenders are Free and available if you wish to access your boat outside of office hours.
The marina has a fuel berth - very helpful for me.
Security is good, although you are obviously a little more exposed on a swinging mooring.
Bear in mind the swinging moorings are only available during the summer - all boats come out onto drystack (or take it home) from Oct onwards.
Last year I opted for the more expensive trailer and forklift mooring - it was about 30% more expensive but I dont have to worry about antifouling, less maintenance, better security, 24 hour, 365 day acess and free water, wash down and shore power facilities.
Hope this helps?
Adam