Vickers 221 Slings, apart from being cleverly named (2 to 1, get it?), are regular Vickers Sling with the addition of a Burnsed Socket and your choice of RED Swivel or standard QD swivels. This simple hardware addition adds considerable functionality and makes for very easy and very fast transitions from 2 point to single point configuration.
These slings are a good deal to begin with considering all the hardware they come with but right now Blue Force Gear is offering them at 20% off. You can check out all of the options and some product videos that will give you a great idea of how the sling works (don’t worry, it is exceedingly simple) at BlueForceGear.com.