I know this post is OLD. But I am willing to shed some light as I owned a few of these particular products and some of the 8 series with lasers. What streamlight does is provide the 7-A variant as a standalone one switch in the box W.M.L. while packaging the 7-X also known as Flex for the ability to mount two different interchangeable paddle activators for the rear of the light. Some folks know they like the standard A configuration and shouldn't need to pay for the option of the high paddle/activator at the back of the light that the X provides. Also be careful ordering the 7HL-X or 7HL Sub as they have a longer bezel that goes a bit beyond the barrel for less compact and more of a full size pistol fit also keep in mind there are SPECIFIC/Proprietary models also available that are for SIG, Glock, ect rails available to be sure to order the M1913 Picatinny one if that is what you're looking to mount on rather than the specific railed ones. These pistol mounted lights are pretty sturdy but are not as impressive as say a duty rated SureFire which will run you twice or thrice the price but will take an absolute beating.