This picture shows the main seal. The seal is teflon coated on one side (the side that rubs agains the flaps or ailerons)  Proper alignment of this seal is very important and requires that some rivets on the plane be drilled out and replaced with a longer rivet that goes through the seal and into the drilled out hole.
This shows the root of the flap and the seal that goes over it.  This seal is attached to the flap and overlaps onto the fuselage.  Like the main seal, it is teflon coated on side that touches the fuselage.

Beryl DShannon claims a 4 to 7 mph improvement in cruise with this kit installed.  That may be true, but I can't attest to it.  I did all sorts of modifications after my  incident and subsequent  rebuild that affected my cruise speed.  I have no idea how much is due to these seals.

They also claim better slow speed handling.  I am sure this is true as well, but as I added M model square wing tips at the same time, I can't say how much the improvement was due to the seals.

The price of the kit was something like $600 in 1995.  Personally, I think the Bonanza flies pretty well without them.  However, as I had to remove and rebuild all of my control surfaces anyway, adding the gap seals on did not take that many more man hours (relativly speaking).  Unless you are regularly flying your plane on the ragged edge of a stall or despartly trying to squeek out all the knots you can, I think there may be better ways of spending your aviation dollar.

This may be folk-lore, but many pilots do not like gap seals because they can cause the controls to become unmovable if they ice over.  However, as I don't go anywhere near icing conditions (and hope I never do), this isn't that big of a concern for me.