Seems like the original poster here though wants to learn about how to make best use of a glide computer, not brand-name recommendations. There is a lot to learn, although best done by doing it (carefully - keep your attention outside the cockpit). I found that transitioning from paper-map-and-whiz-wheel to a computer allowed me to shift from over-cautious glide-guesstimating to a more precise glide envelope around each landable airfield on the route, resulting in my flying a lot more XC. At the price of occasional landouts of course.

Alternate way: If you want to learn how to apply McCready theory using a generic PDA, I'd suggest getting CONDOR - the competition soaring simulator, which has one (displays push/pull on the e-vario). You can then fly multiple flights at different MC settings, in identical weather, and see what the result is, on, for example, final glides. You can save igc files from previous runs and fly "against" them as ghosts (and see who gets home, who doesn't, and who gets home fastest). Once you understand zero wind MC theory, do runs at different MC settings up and down wind. There probably is a CONDOR scenery for where you fly (or have flown). It's interesting to do in the winter, and I find that I have little rust to brush off in the spring.

Why get a book (though I have many, and read them all - Advanced Soaring Made Easy - 3rd Edition by Bernard Eckey is my current favourite, available from many fine vendors in North America) when you can live the experience in the comfort of your own home?

"I hear and I forget; I see and I remember; I do and I understand." Confucius

Do; Understand. Then, with the benefit of practical experience, you're prepared to look at different flight computers to find one that speaks to you.

Dan
2D