The majority of mine are mobile. The base under my TS came with it from Grizzly. Very sturdy. I recently made a MB for my router table. I intentionally used larger casters to help with the height. I hate stooping over and my back gets tired and sore from doing so.
I prefer mine to be directly underneath the tool(s). Less chance of "tripping" over them if needing to walk around them. I also prefer swivel locks.
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