I'm not sure if any have actually failed but, from an engineering view, the back action sidelocks do provide for a stronger action and, since the leaf spring and lock components lie flat against the sideplates, really do not need any more inletting space in the stock than a standard H&H style sidelock. No more wood is removed by utilizing a back action design.

The only difference between a Bar Action and a Back Action is the position of the leaf spring; one is pointed toward the rear and the other toward the front. In my opinion, the bar action gives the best sear/tumbler engagement angle and can be adjusted much better. Bar Actions, on the downside, require much more inletting along the acyion bar. This is why some of the older guns employed a Greener Crossbolt on their Bar Action sidelocks. I think that modern metals offset a lot of this. That being said, if I had the means to order a bespoke sidelock, I would do so with a back action sidelock design.