They're pretty darn heavy for a stock. I've found that the ACS works well for a "precision" type AR and the STR works well for lightweight AR's, both keeping the weight to a minimum and costing less than half of what the UBR does.
Looks cool but there's not enough of a benefit over even the basic MOE. Probably has a lot to do with shooting style I suppose. Im used to to shooting commie weapons so I often square up my shoulders. This allows me to not have to extend the stock out too far.