Buddy of mine has something that looks like the Stack Pack on his P27. It does indeed make stowing the main extremely easy - drop the main, zip it up. A very quick and easy job, which to be honest I envy!
In the interests of full disclosure, two potential drawbacks. First, as the StackPack stays on the mast, it is (arguably) less attractive to have these covers hanging down while you sail. Something to consider if you spend hours gazing lovingly at your boom while under sail. Personally it never bothered me.
Second, the boats co-owner is convinced that it effects their racing competitiveness. The rest of us are not convinced and, although I love my P323, try as I may she's not that competitive anyway!
(Disclaimer: Not linked with Dolyle or any sail loft!! :-))
