Do not be surprised if you need to do a little filing and scraping on the latch bar that locks the X200 into your XDs rail locking slots. The latch bar is made of a non-meta materiall and you can shave with a small file and sharp knife to debur it so as to release the unit from your gun with little effort.( If you notice it being a little tight.)

And on my DX-45 service it was REAL DARN tight I needed gloves to hold the release tab to get it off before doing the slight rework.

Going to submit a work invoice to Surefire.

Also note you have to snap the battery cover on. Use care to keep them alined as thay install tightly and if mis-alined it you can break them off so says the instruction manual.

I did get mine on. Anyway it is a really nice bright light I have the X200B. Wide Beam Model.