Thanks for the heads up, I've added the following text to the guide:

Note: There are also ETH fees associated with transferring tokens from Ethereum to Polygon and back.

Although once your assets are on the Polygon network, your MATIC fees are minimal.

Moving crypto assets between chains is always going to be expensive.

But once your assets are on the Polygon network and being used for DeFi, then you will save some money.

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