help with ryobi electric/brush cutter

I have the Ryobi electric powerhead and noticed that the manual said you could use any attachment but do not use the brush cutter attachment. Of course, I need the brush cutter attachment.
You can use the pruner, which is a chainsaw that can cut 6" limbs, but the brush cutter which is used for 1/2" pulpy weeds/brambles is not recommended.
I called tech help about this and asked if the reason was because there was more risk of cutting the cord with the brush cutter [the pruner being elevated and not near the ground].
Tech help did not have a great answer and was not even aware of the electric powerhead being available. However they did say that the rpm of the electric is less than the gas, and that if you hit something big, it might break the shaft. As if the gas powered one could not hit a rock and break as well.
In the manual, it says to not use the brush cutter because it may result in 'personal injury, electric shock' and other hideous things.
I think this is just a ludicrous warning if you can put a chainsaw on the end of a stick and run *that.
Does anyone have an insight on this?
One other thing, I noticed that the 'tri blades' that go on these things are fairly dull. It seems like you could compensate for the lower rpm by sharpening the blade.
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