I have the multimaster and think its a great tool. It is pricy though.
Do not get the cordless model.
I don't have teak decks, so haven't used it for that, although I think it would do a good job of it. Depends on what your time is worth as far as the cost. For me I used it to help sand my sole and bulkheads for varnishing, cut wood and metal, grind, polish, and to other jobs. The attachment for dust collection is poorly done. and same as some of the sanding
attachments. I have had to replace the velcro pads several times.
Nice heft to the tool.
I wish festool made one, cause I have no issues with any of their tools.
My 2 cents is, if you have a need for the tool, get it (and who would't ?) and if not go thru it the old fashioned way and hard work.