I have refilled these tanks like this and would like to recommend wearing safety glasses. I have had the propane come out a little and it freezes like freon or anhydrous and would not want to get it in your eyes.
I think it's a terribly neat (but expensive to use) idea. We use thoes little canisters for camping all the time, so it wouldn't be too bad to get one. But I would cringe every time knowing how much it was costing me to run it!
One of the re-fill adapters is on my shopping list.
It will definitely be more expensive to operate than a comparable gasoline model, but I don't think most users would notice it. Even for me; I mow/trim just under 1.5 acres and even though I use my 2-cycle string trimmer 3-4x a month during the mowing season, It's only about 30min of use per month. If one little propane cylinder lasts even close to 2hrs like the manufacturer suggests, one or two cylinders would carry me through the mowing season. No need to worry about stale gasoline/premix sitting around, carbs and sparkplugs fouling, gasoline leakage, etc.. I think it's a decent approach for the average homeowner.