Adjustable legs are NOT a bad thing per se. They allow one rack to fit more than one bike with no redesign. What they do require, however, is that the rider mount and adjust the rack correctly and completely, tighten the nuts/bolts and then periodically chck those bolts during a trip. This latter bit, checking, is a safety aspect that should be done with any bolt on te bike anyway. A bit of blue Locktite on the bolts and you're good to go for the most part.
Remember that hundreds of people have toured with "adjustable", sub-$50 racks over the last few decades - notably a few round-the-worlders in the 70s and 80s and more during 1976, more hundreds on the TransAm cross-country tour.
Generally, the difference between expensive racks and clones/inexpensive ones, imo, is price or weight limits (carrying capacity and/or weight of the rack itself) or both. I've had one $200 rack and a number of sub-$50 racks. All did the job so long as they weren't overstressed - even the expensive one failed when I overstressed it.
You can "get away with" a lot less "rack strength" if you're only going to ride on paved roads than if you're going to go off-roading.
Loading your panniers should be the same whether it's a cheap rack or not --- keeping the weight low and as close tot he center of the wheel as possible will put the least strain on the rack itself.
Last edited by drmweaver2; 08-22-12 at 11:20 AM.