Below are just some collected discussions on the topic of these two stabilizer options. As usual, each has its proponents and detractors...
GLIDECAM vs. MERLIN for the XHA1
GLIDECAM 4000 on DVforums
MERLIN or GLIDECAM: DVXuser
And here is an HV30 FORUM DISCUSSION about the Merlin, the 4000, and a couple other competitors.
And last but not least, a BLOG POST by a fellow who loves the Steadicam Merlin for use with his XHA1 much more than his old Glidecam. That fellow is, of course, Steven Dempsey, one of the more well-reputed users of the XHA1.