Yes. If you don't know how the script executes something don't use it because ultimately you are responsible for the end result. Also just because something gets 5 starts form a lot of users doesn't mean those persons are the best possible people to give those ratings. The most dangerous things are those that apparently work at first but neglect something nontrivial down the line. They work at first but don't really work at all giving you false sense of security because it worked at first sight*, About 90% of all scripts are pure crap.
The thing is expressions are not MEL in the strictest sense. They are MEL evaluating the dg connections. Now MEL has access to the full run time, on contrary dg nodes should only be dependent on their connection slots. Now there's a very high temptation to just go directly and fetch some information after all they don't differ much. But in doing so you scrap the entire dg's inner workings and one of the thing you loose is anonymity.
See expressions are preprocessed to make for the data slots whenever you write:
someobject.SomeAttribute
the expression engine goes a head and replaces this with
.I[?] or .O[?]
which is a connection. Your not actually referencing any name yoru referencing the container it just gives you a quick shortcut for making that connection. Now this is all spiffy and cool. But MEL scripting does the same thing so having:
someobject.SomeAttribute=10;
setAttr someobject.SomeAttribute 10;
is superficially the same thing but formally they are actually:
.O[0]=10;
setAttr "someobject.SomeAttribute" 10;
which is WAY different, see parsing rules notice in the later case a mel command and its followed by a implicitly assumed string. Now strings are just whats typed in the thing connections aren't they are wahts actually connected. Now if you go and rename someobject the pure connection stays on target but the string STILL reads "someobject.SomeAttribute" and you have problems.
Great deal of power can be gained by sidestepping the dg evaluation rules, and much can be lost. With power comes responsibility.
*usually the thing is what makes easily sense is not right, because theres lots of unexpected things ahead. So a measure of why so convoluted can give insight on how experienced the maker is, thenagain it can also be a sign of inexperience go figure. 
