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I use body-only RRS L-brackets on my 5D, and previously did with 30D and 40D bodies. I also use RRS L-brackets with 1D-series bodies. Generally, I'll put on a bracket when I want to use a tripod or monopod, and just leave it there until I decide to take it off - usually because it fits better in a bag (as Daan mentioned), or because it just won't be used for a while, like when I'm shooting handheld or with a big lens that has its own RRS plate. I don't have any problems when shooting handheld over a RRS L-bracket. I have big hands.
Keep a hex wrench handy, and you can take it off in a flash. I 've used a body+grip with other L-brackets and simple bottom-only plates, and stability is only a problem when the grip isn't securely fastened. Generally, when you're using the L-bracket, you're in relatively controlled conditions, and so the extra power and portrait mode 'handle' provided by an optional grip isn't so important.