So it worked, needed to wait 5 blocks (confirmations) to "Jam" the funds.

I then moved from Jar "A" to Jar "B" in a collaborative transaction which cost me 13.5K Sats (around $8). I used all the defaults:

8 collaborators, absolute fee: 72,840 Sats, Block target 3.

I'm sure defaults have some wiggle room.

For large sums this is worth it, for small sums, probably not.