This is a pretty cool idea! I could see myself using a potion like this while mining or exploring structures, and I imagine this would be very helpful in survival mapmaking.
I don't think echo shards should be the material though. As cool as this effect is, as long as echo shards are rare and nonrenewable, I'm not gonna use them on this potion. This effect should be much more accessible imo.
Rebounding on demand with milk is a really clever interaction, though it might end up being a bit powerful depending on how long it lasts. I'd say the standard 3 minutes (8 if extended) would work. Also, I assume drinking the potion again would create a new save point instead of extending the duration of the current one. Otherwise, that might be a bit OP.