Mud/Silty substrates

Evening all.
I'm currently planning a complete overhaul of the tank that houses my Orientalis(to seperate them), and was thinking about substrates. Theres a quote on the CC caresheet which is of particular interest to me;

Always the water is cold and quiet, in the shade of grass, with a mud bottom free from stones

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I use tetraplant complete substrate almost exclusively in my planted tanks. For anyone not familiar with it, its a fine grained sandy/muddy substrate. I recently observed(having re filled a plant pot and not having any gravel left to top it with) that they seem to enjoy 'playing' in the un topped substrate. The female in the tank spent several hours sat on, and snuffling around in the the 'mud'. Perhaps natural foraging behaviour?
Has anyone observed similar behaviour before(I should mention that the newt in question was shop bought, and to my knowledge wild caught)? Has anyone tried using a similar product as substrate without topping it off with sand or pea gravel?

I realise it will make quite a mess, but the filter will have a seperate housing with the intake holes well off the bottom of the tank to minimise sediment getting sucked in. Feeding will be via a trench at the front of the tank with no substrate to make removing left over food easier. The tank will also be heavily planted with Marsilea Quadrifolia, Eleocharis Aciculatus and Sagittaria Pusilus('four leaf clover', 'Dwarf hairgrass' and 'Dwarf Sagittaria' to give their common names), which I'm hoping will emulate their natural habitat as closely as possible, should tolerate the water conditions and temperatures and also help keep the substrate in place.