It's a little pricey ($85 for the Chimp), but it seems like it would be quite useful. Also, one video I saw of the Silverbac showed that with a full hopper, the entire grill can be a bit "hopper-side" heavy. It's in no danger of tipping over, but the video showed that if someone inadvertently leaned on the top of the hopper, it could happen.
The Chimp (the model I am looking at) does have a lower center of gravity so this is much less an issue, but I'm thinking of getting the shelf just to mitigate that potential issue.
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