a question for those with seat rail extenders

i was searching and all the threads i read dealt with the kenny brown extenders. people were saying that with these the seat drops a bit lower when they are extended. is this true and how much does it go lower? i really want a set of these but they are expensive so i was also wondering if anybody had bought the ebay ones.
http://cgi.ebay.com/ebaymotors/94-9...ryZ33701QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
and if so how do you like them? do the ebay ones drop lower as well?
thanks for any information