I will most likely be on 40 or 20 meters.
That makes a big difference in this case.
On 40m using the mast as part of the radiator improves efficiency. On 20m adding 10' to the
portion below the loading coil may make the antenna too long to tune properly. I don't
remember what the minimum length is where the slider makes contact with the coil, but I
think it is close to 8' long (so 10m uses little or no inductance.) The combination would
have a minimum length of 18', which is longer than a quarter wave on 20m. But an 8' mast
And if your objective is to experiment with antennas, this might be one aspect to look at.
But the radials should attach where the coax shield does, not to the bottom of the mast.
Otherwise the shield ends up having some RF voltage above ground, which aggravates
common mode currents.