Using the BinaryDelta tool

We have an app that uses Sparkle and has some large data files that rarely change. Our customers
have complained about the time and bandwidth when downloading the updates.
My understanding is that Sparkle supports delta updates using the
BinaryDelta tool. Some questions:

1. Is the delta updates feature "ready for prime time"? I can find
very little information it. Is this still considered experimental? The
code for the BinaryDelta tool only exist in the download on GitHub, and not
in the 1.5b6 version on: http://sparkle.andymatuschak.org/ .

2. Do we need to supply delta updates from every past version to the
present? Or can we supply a single update like the "Mac OS X combo updater"
that updates any 1.x (e.g. 1.0, 1.1, 1.2, etc.) to the most recent version?
We want to avoid forcing users to run a series of delta updates to
get themselves current.

3. Are there any examples of what the appcast should look like for these
delta updates? In response to another question, Andy said to look at
http://nightly.webkit.org/builds/trunk/mac/rss for an example, but it is not
clear (at least to me) how this link is useful. A more explicit example
would be helpful.

We love Sparkle, and making it able to do "combo-delta updates" would be
even better. Thanks for any help you can provide.