I've been using quiver killers for two years now, primarily in the back country - they have a few issues, but nothing too major. I switched over to binding freedom's slotted inserts last year for a new pair of skis and found them much easier to work with (and they are cheaper!). When properly installed with loctite, i've never had a loosening issue (besides with free rides). I'm ~230lbs and ski 20-30 days a year pretty aggressively.
Downsides:
*Don't work with free rides - for some reason, no matter how much loctite i put on the screws and how tight they are, free rides toe piece always come loose. Two friends of mine have had this same issue.
*Make sure to use loctite
*Make sure to let the inserts sit in a cup of acetone before installing them, as sometimes the OEM doesn't de-grease them
Upsides:
*I didn't have to buy another pair of bindings for my wife, just skis/skins (she only tours a few days a year)
*Much easier to bring multiple pairs of skis traveling and lower risk of breaking bindings in baggage
*Easy to replace a broken dynafit heel piece in the backcountry
*Can swap out alpine bindings with dynafits on my big skis for resort days
*Don't have to have an extra pair of bindings for rock skis
*Lower commitment to buy skis. If you mount yourself, its ~$30/pair to mount with inserts, much cheaper than the $300-$600 cost of new bindings