In my experience I get more attention paid to the demo when i read it. Theres is nothing wrong per sa with the pre-recorded one but I personally feel that my demo voice is more authoratative. Reading that, some here may think i'm being above my station but thats what is needed IMO. On a lively flight to TFS or PMI, you need to make sure it's loud and clear and the PRM doesn't always achieve that. And pre-recorded funcards/sales PA's just scream that the crew can't be arsed.
Some crew admittedly shouldn't be let near a PA and I cringe at PA's made by some of my colleagues. Ideally, PA's should be fairly short and snappy and made at the discretion of the crew. For example, a PA for the bar/food service shouldn't list every product in the brochure but one or two crew members do.
The number of PA's are sometimes necassary, sometimes not. Ultimately, we all, generally speaking, pay too little for our fares and this has to be made up through onboard sales. On my flights, the full lot will get read on a longer flight as they can be spaced out nicely but on shorter flights I make sure they are condensed and sometimes tagged onto another PA. Again, on a busy longer flight I might combine a 'final drinks' PA with something that is definitely practical......i.e landing cards.