i sit when i play, so X stands are the bane of my existence.. if i have to use one, the heavier duty ones are indeed the better.. i wouldn't use one for a significantly heavy board though. I've got two of these:
http://www.zzounds.com/item--ULTVS80
which solve the knee space issues, and are actually reasonably sturdy, but my complaints are:
. no floor space for pedals
. 2nd tier is something rube goldberg would consider overly engineered, and adds 2" to the height of the lower board
. the locking mechanism that holds the stand height breaks easily
. when set up, the stand - in any configuration - is not level.. doesn't affect performance, but is an eyesore for me
next time i buy stands i'm going with a K&M. I've gotten a few of their smaller solutions and holy crap it's well made stuff.. something like this:
http://produkte.k-m.de/en/Keyboard-stan ... d-aluminum