How I use SeeYou mobile for final glides (when I get a chance to do
them):

With my chosen arrival altitude and my/or the computer's best
estimates of the wind set, then in the likely last thermal I use the
usual McCready/Cochrane considerations plus my personal wimp factor
to decide when to leave the thermal and to judge an appropriate
starting McCready setting. This is just to get in the ballpark of
when to start the glide.

Next, as I start the glide I take note of the required LD (SYM
calculates this to the arrival altitude) and as long as this number
stays the same or gets smaller then I am on glide or can speed up
respectively. If the number gets bigger I have to slow down or
climb. The required LD is wrongly named in SYM - it is actually the
glide angle with respect to the ground. All glide angles converge at
the destination so any glide angle that I can keep constant will
bring me to home at my arrival reserve altitude. This is independent
of any errors in wind/polar/bugs. I never have understood why most
glide calculators seem to work on altitude difference displays
resulting glides vertically parallel to the starting glide angle when
proportionately less altitude difference is required as one gets
closer to the destination.

(I don't find that the method recommended in the SYM manual of
comparing Achieved LD with Required LD is any good because the
Achieved LD varies so much in a much shorter time scale.)

John Galloway