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I did email K&H a couple weeks back asking why they discontinued it and if they ever plan to offer it again. This was their response...
"We did not sell enough of the RNG300 to keep selling.
We were getting enough orders to keep making the RNG200.
I will pass your suggestions along to the product team.
I hope we can bring this item back in the future.
I hope you have a wonderful day."
I'm not holding my breath they will bring it back, but maybe if they get enough questions on it they might reconsider? Wishful thinking.