IMHO speedskims are superb, if they are used correctly. The original ones are for flattening off your 1st and 2nd coat with the new blades being used to start off the trowelling up process, me personally I can't get a satisfactory finish with them but that's when my plaza trowel comes out and finishes off the job. Saves me about 40/45 mins a gauge and not even 75% of the work I used to do. 36 years in the trade and after all this time I've learnt that plastering aint that hard on my body, just wish they had been around years ago. Having said that some hate them, not sure if they are expecting too much from them or they are using them at the wrong time.
If you do get one/some read the how to guides on their website, and remember you will have to plaster differently.