Spraying skim is not the best example of machine plastering. If you browse you will find many have tried to spray skim before deciding its not for them, but you will also find a much greater number of people who have bought Ritmos and never looked back.
The Ritmo is a 230v mixing pump you just plug straight in and get going ( once you are confident) The more gear you are using the more beneficial and even essential it becomes.
If you are going down the route of machine plastering then you will be changing the type of jobs you do slowly over time, you will not be so interested in over boarding and skimming, or making good a few walls , traditional render etc etc you will be looking for jobs you can exploit the machine. I.e Mrs Jones wants her garden walls plastered, you will be enthusiastically promoting a finish that you know goes through your machine. Most customers go by the expert advice or the better quality option and before you know it the machine is being used as often as your old mixer was.